Corrosive + Subclassing: A Dangerous Combo That Needs Attention

MeridiaFavorsMe

Let’s talk about something that’s going to be a huge issue next patch for anyone hoping to enjoy PvP in even the slightest way. Corrosive is currently the strongest PvP ultimate in the game. It's widely used to ignore incoming damage while simultaneously going on the offensive. Although it's been around for years and functions as a get-out-of-jail-free card that also enables massive damage output, it hasn’t received much attention—mainly because it’s used for dueling or solo play. Also, since it’s limited to one class, it’s not commonly run in large group settings as a damage ult. However, it can still be extremely overpowered in small group play or when used in combination with sets like Cryptcanon.

But the next patch is going to make this situation much, much worse.

Once the changes to subclassing go live and Corrosive remains unchanged, every ball group damage dealer will be able to slot it. Right now, the only real downside to Corrosive is that you can’t generate ultimate while it’s active. But this is a non-issue for coordinated ball groups, which can simply play defensively until it’s back up—or even use sets that instantly generate another Corrosive when the first one ends.

There will be no way to counter any ball group that takes advantage of this. All incoming damage will be capped at 3% of max HP, which is easily outhealed by even minimal cross-healing. At the same time, all Corrosive attacks ignore resistance entirely, letting anyone running it melt even the tankiest builds. Imagine someone popping Corrosive and parsing on you while an oil above them ticks for less than 2k damage. Ball groups will have more damage output and more survivability than ever before—and nothing that currently counters them will remain effective if they play properly. They’ll be virtually invincible.

Corrosive is simply too powerful in every PvP scenario.

Need more damage? Pop Corrosive and ignore all enemy resistances.

Need to survive? Pop Corrosive and limit incoming damage to 3% max HP.

Want both at the same time? Corrosive.

It’s overtuned:

The cost isn’t high enough.

The duration is too long.

The buffs are too strong.

There’s no scenario where it’s a bad choice in PvP.

Of course, some people will disagree—mainly those who want to abuse it next patch or those already using it and don’t want to lose that advantage. And to be fair, I get it. I’m not a fan of nerfs either, especially if it’s something I enjoy playing. But Corrosive is too much to allow for the health of the game.

I understand ESO isn’t known for implementing specific ability limitations, but something has to give. Maybe allow DKs to continue using it, but not make it accessible through subclassing. I wouldn’t mind if it were restricted to PvE, but it’s not even used there since there’s no real need for 100% penetration. Even if you allowed corrosive to ONLY ignore 100% of enemy resist it would still be strong, but allowing that and reducing your incoming damage is overloaded.

If you don’t agree now, you’ll see once the patch drops. I just really hope something is done. PvP is already in a slow spot, and Corrosive will make it worse.

tomofhyrule

Honestly, I think Corrosive is too overtuned.

You can shrug off 97% of damage and all of your attacks go through armor? Yeah, that's a lot.

The problem is that since people were using Magma to cheese the Archive, they nerfed the Magma morph to also not generate ult while active. Which, fair, that is a cheese, but that means that Corrosive is 100% better than Magma in every way.

I could see things like a cost increase, or even take the mit (for Corrosive only, not Magma) down to 50% to try to balance out the two morphs and make it not as oppressive in PvP, especially since people are easily going to be able to pair Corrosive with double proc bows now (which is its own problem).

RealLoveBVB

There are several threads incoming like this, once the update is live.
The game will sink in Chaos the next months, till they nerf everything to the ground.

Desiato

This is the problem with subclassing. Arguably all classes have op abilities/passives that offset each other, but are untenable when combined on the same character.

I don't think corrosive is currently OP with the ult gen we have available, but subclassing is probably going to change that.

So much disruption for something that will be a fun novelty for a few months before something that is supposed to give us more options counter-intuitively results in fewer and we're back to square one, but worse.

Teeba_Shei

Corrosive has been a problem since way before subclassing. The unique armor penetration allows you to completely ignore penetration as a stat and stack into other things. It probably shouldn't have any defensive component on it at all if its going to retain its armor penetration.

Desiato

Teeba_Shei wrote: »

Corrosive has been a problem since way before subclassing. The unique armor penetration allows you to completely ignore penetration as a stat and stack into other things. It probably shouldn't have any defensive component on it at all if its going to retain its armor penetration.

Yes, but if your opponent recognizes it and is prepared, it is easy to counter just by being evasive. It's not like corrosive is the scourge of Cyrodiil.

The_Meathead

Corrosive doesn't bother me in current form (halts Ult regen), but we'll see how it goes once Subclassing is here.

I think Grim Focus x2 is my biggest fish to fry along with (not because of Subclassing) Rush of Agony and Ballgroups stacked heals/shields still trainwrecking Cyrodiil, but I'm sure all number of outliers are gonna spring up very soon because Subclassing got almost zero balance in regard to PvP. It might have gotten literally none.

It feels like they bit off so much more than they can chew with this and PvP is always the last one at the table to get served when it comes to balance, particularly now that they're putting so much time into Vengeance.

The_Meathead

RealLoveBVB wrote: »

There are several threads incoming like this, once the update is live.
The game will sink in Chaos the next months, till they nerf everything to the ground.

I'm honestly dubious how much they're even gonna bother.

I feel like we're likely gonna get an announcement at some point that the Vengeance campaign is for people that want any sort of balance at all while everything else is just hands-off Wild Wild West craziness, similar to what WoW did at one point in regard to WPvP.

Mind you, that's not my preference, but it seems where we're probably headed.

xylena_lazarow

It's one of those things that really clowns on unaware players, but is pretty easy to avoid if you know what to look and listen for, and has a very long downtime. I haven't seen any one shot clown builds, just a couple normal Bash/Reverb/Corrosive style builds that seemed to do well into the meta Burstplar variants (but not into Storm Calling builds).

Seemed pretty balanced, it has plenty of counterplay, the downtime demands patience, Earthen Heart is kinda weird and generally hard to fit on builds. Something could show up, but right now I don't see Corrosive being a problem or even widespread. Ball groups are their own problem and are already unkillable, nothing changes there.

Urzigurumash

Corrosive should only buff skills with a melee range. Before Hybridization this Ult was exclusively for PvP StamDK, and the 1 and only non-melee range skill we ran was Flames of Oblivion, which was Flame Damage and not buffed by Corrosive since it only ignored Physical Resistances.

However, we also suffered numerous limitations that no longer exist. We were essentially dependent on Dizzy Swing which is why the class was unpopular both with noobs and also high tier duelists and such whose opponents never die to anything which can be blocked and dodged outside of the .5s it takes to break free. (or so I'm told)

So there will be many cases where many things are overpowered, but for now by far the most logical choice is to

Limit Corrosive's Penetration to Melee Range Skills only.

Urzigurumash

xylena_lazarow wrote: »

It's one of those things that really clowns on unaware players, but is pretty easy to avoid if you know what to look and listen for, and has a very long downtime. I haven't seen any one shot clown builds, just a couple normal Bash/Reverb/Corrosive style builds that seemed to do well into the meta Burstplar variants (but not into Storm Calling builds).

Seemed pretty balanced, it has plenty of counterplay, the downtime demands patience, Earthen Heart is kinda weird and generally hard to fit on builds. Something could show up, but right now I don't see Corrosive being a problem or even widespread. Ball groups are their own problem and are already unkillable, nothing changes there.

You say BurstPlar in lots of posts, this isnt a well known term. Plar has tons of burst on live with Aedric Spear's strong passives after the change to Burning Light, but can you explain what specifically a BurstPlar is?

xylena_lazarow

Urzigurumash wrote: »

but can you explain what specifically a BurstPlar is?

Burst builds that mostly stay in their Restoring Light circles while setting up combos, resembling a Templar playstyle. The buffs to Restoring make it the strongest defensive line in PvP. For open world the most popular version will probably be Restoring/Assassination/Animals, but Grave Lord, Aedric Spear, and Dawn's Wrath also appeared a lot.

Urzigurumash

xylena_lazarow wrote: »

Urzigurumash wrote: »

but can you explain what specifically a BurstPlar is?

Burst builds that mostly stay in their Restoring Light circles while setting up combos, resembling a Templar playstyle. The buffs to Restoring make it the strongest defensive line in PvP. For open world the most popular version will probably be Restoring/Assassination/Animals, but Grave Lord, Aedric Spear, and Dawn's Wrath also appeared a lot.

I see, thank you. So no room for Earthern Heart. Definitely a major consideration. There's no top tier skill in the line except Fossilize and that skill is also the only min-max compliant way of keeping up Mountain's Blessing for most playstyles.

TheLoreMaster420

I agree, so let's talk about some actual solutions. The ult essentially gives you an infinite amount of penetration. Even players who go above the normal pen cap and decide to go to, lets say 50k pen (so even if they are afflicted with major and minor pen they are still at max resist) take the same amount of damage as someone with 0 resistance.

That along with the fact that it allows you to only take 3% max HP damage is insane. I think a good work around would be to remove the pen, that way people can still use it for it's main purpose in PvE of surviving through things you normally can't, or even giving it the same 3% max HP damage taken and giving the person who uses it a unique 5k extra pen while active. I think this is still really strong, but at least it brings it much closer to some sense of being balanced. Something like 10k pen still seems absurd and overpowered to have on an ult that also makes you more tanky than any other ult in the game. While 5k is still extremely strong I think it's a good starting point for balancing it.

Teeba_Shei

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

RealLoveBVB

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

randconfig

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

Exactly, if a player has 33k armor (I think that's the cap), then they have 50% damage reduction. So a 46% damage reduction for ignoring armor just means the set allows you to deal 4% more damage.

For a player ultimate that costs 200 (I think that's how much it costs), bypassing 50% damage reduction sounds good, until you factor in all the free sources of penetration in the average character build, and factor in the fact that there are many players that don't optimize to get 33k armor in PvP. So you'd be likely fighting someone with minimum armor around 11k, meaning the offensive portion of the ultimate just grants you a 17% damage buff for 10 seconds.... The defense portion just reduces incoming attacks to 3% max health are most, also just for 10 seconds...

The main use for the ultimate is if you wanna try to 1vX, only being offensive during the ultimate, running around terrain/objects during the time it takes to build up 200 ult, which is not broken.

And it makes DPS builds actually able to hurt tank builds that have armor over the 33k cap preventing various sources of penetration from bringing them below 50% damage reduction in PvP; this ultimate negates that for 10 seconds... So still not op.

randconfig

tomofhyrule wrote: »

Honestly, I think Corrosive is too overtuned.

You can shrug off 97% of damage and all of your attacks go through armor? Yeah, that's a lot.

The problem is that since people were using Magma to cheese the Archive, they nerfed the Magma morph to also not generate ult while active. Which, fair, that is a cheese, but that means that Corrosive is 100% better than Magma in every way.

I could see things like a cost increase, or even take the mit (for Corrosive only, not Magma) down to 50% to try to balance out the two morphs and make it not as oppressive in PvP, especially since people are easily going to be able to pair Corrosive with double proc bows now (which is its own problem).

Oppressive in PvP?? That's just not something I've seen personally, the ultimate is good, but it's a damage boost around 17% for non-tanks while reducing incoming damage to 3% max health for 10 seconds. Pretty sure bomber builds can just delete entire groups of players with a single ultimate, and for single target damage, the barrage bow ultimate is way more oppressive than this. So I just don't get the calls for nerfing it, especially since the DK class is already being nerfed in the incoming patch when it's the most lackluster/boring class in the game.

randconfig

Desiato wrote: »

Teeba_Shei wrote: »

Corrosive has been a problem since way before subclassing. The unique armor penetration allows you to completely ignore penetration as a stat and stack into other things. It probably shouldn't have any defensive component on it at all if its going to retain its armor penetration.

Yes, but if your opponent recognizes it and is prepared, it is easy to counter just by being evasive. It's not like corrosive is the scourge of Cyrodiil.

Exactly, you literally just walk away/heal/damage shield for 10 seconds... I don't even play DK because of how lackluster the class is, and the one thing they have going for them, people are wanting it to be removed lol...

Major_Mangle

There will be no way to counter any ball group that takes advantage of this

Ye no ballgroup worth its salt will be running corrosive, much better tools/skillines to use for medium-/larger groups. In smaller setting (anything below 4) then corrosive does have some value, same for battlegrounds or generic solo play. Corrosive as an ultimate is fine ever since they prevented you from gaining ultimate while it´s active (you can thank Cryptcanon for that balance change).

randconfig wrote: »

Desiato wrote: »

Teeba_Shei wrote: »

Corrosive has been a problem since way before subclassing. The unique armor penetration allows you to completely ignore penetration as a stat and stack into other things. It probably shouldn't have any defensive component on it at all if its going to retain its armor penetration.

Yes, but if your opponent recognizes it and is prepared, it is easy to counter just by being evasive. It's not like corrosive is the scourge of Cyrodiil.

Exactly, you literally just walk away/heal/damage shield for 10 seconds... I don't even play DK because of how lackluster the class is, and the one thing they have going for them, people are wanting it to be removed lol...

Wouldn´t say it´s "easy" unless you´re a sorc that can either negate the DK or streak away. An acuity DK has by far the highest nuke/burst damage in the game and nothing else really comes close. If the DK execute their combo correctly and you haven´t popped an immovable potion or got far enough away it becomes a pure stat check that determines if you survive or not (and unless you´re a fully fledged tank and/or sit at 45k+ HP you won´t survive most of the time). The problem is rather the synergy with sets like acuity and mythics (like the major force one ZOS are adding next update) more than the ultimate itself.

Anyway, while corrosive isn´t a bad ultimate, the rest of the skilline isn´t that impressive in my opinion. Unless you plan to play around corrosive entirely (which most likely also forces you into an acuity setup to kill people) then I´d say there are better and scarier combination of skillines to choose from.

The_Meathead

randconfig wrote: »

Desiato wrote: »

Teeba_Shei wrote: »

Corrosive has been a problem since way before subclassing. The unique armor penetration allows you to completely ignore penetration as a stat and stack into other things. It probably shouldn't have any defensive component on it at all if its going to retain its armor penetration.

Yes, but if your opponent recognizes it and is prepared, it is easy to counter just by being evasive. It's not like corrosive is the scourge of Cyrodiil.

Exactly, you literally just walk away/heal/damage shield for 10 seconds... I don't even play DK because of how lackluster the class is, and the one thing they have going for them, people are wanting it to be removed lol...

This is kinda where I am. When I die to Corrosive every once in a while, my first thought is, "UGH, why didn't I see that sooner?" not "Ugh, SO OPed!"

The only time I remember it being legitimately problematic was when Oakensoul first came around and (pre-Nerf) gave Major Heroism while you could still generate Ult inside Corrosive. People could run it with a Minor Heroism set, Bloodspawn, etc, and churn out a Leap inside Corrosive. That was a bit much.

I really don't think Corrosive is gonna be among the biggest outliers when Subclassing hits, but we'll see pretty soon.

The_Meathead

Urzigurumash wrote: »

Corrosive should only buff skills with a melee range. Before Hybridization this Ult was exclusively for PvP StamDK, and the 1 and only non-melee range skill we ran was Flames of Oblivion, which was Flame Damage and not buffed by Corrosive since it only ignored Physical Resistances.

However, we also suffered numerous limitations that no longer exist. We were essentially dependent on Dizzy Swing which is why the class was unpopular both with noobs and also high tier duelists and such whose opponents never die to anything which can be blocked and dodged outside of the .5s it takes to break free. (or so I'm told)

So there will be many cases where many things are overpowered, but for now by far the most logical choice is to

Limit Corrosive's Penetration to Melee Range Skills only.

While I'm not a proponent of nerfing Corrosive itself, this^ would be a very good idea in general and particularly with Subclassing on the horizon.

SolarRune

Just need to accept it's goign live as is, there have been plenty of similar threads on the PTS forum pointing out similar issues with other skills and they have had very little impact on what is going live in a couple of weeks. The game will be "fun and interesting" for a period of time while things are worked out on live rather than in testing, like it should have been.

Teeba_Shei

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Urzigurumash

Teeba_Shei wrote: »

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Ok so Trees Ult needs a nerf cuz it heals so much better than Almalexias Mercy? Since when do 5 Pieces equal Ults

Urzigurumash

The_Meathead wrote: »

Urzigurumash wrote: »

Corrosive should only buff skills with a melee range. Before Hybridization this Ult was exclusively for PvP StamDK, and the 1 and only non-melee range skill we ran was Flames of Oblivion, which was Flame Damage and not buffed by Corrosive since it only ignored Physical Resistances.

However, we also suffered numerous limitations that no longer exist. We were essentially dependent on Dizzy Swing which is why the class was unpopular both with noobs and also high tier duelists and such whose opponents never die to anything which can be blocked and dodged outside of the .5s it takes to break free. (or so I'm told)

So there will be many cases where many things are overpowered, but for now by far the most logical choice is to

Limit Corrosive's Penetration to Melee Range Skills only.

While I'm not a proponent of nerfing Corrosive itself, this^ would be a very good idea in general and particularly with Subclassing on the horizon.

Thanks, Ive written more about Corrosive than anybody in history, theres an argument between me and Static somewhere from couple years ago that gets into some deep philosophy about it

Static if youre out there reading, you finally got Corrosive on StamSorc 😆

Teeba_Shei

Urzigurumash wrote: »

Teeba_Shei wrote: »

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Ok so Trees Ult needs a nerf cuz it heals so much better than Almalexias Mercy? Since when do 5 Pieces equal Ults

Does wearing Almalexias Mercy reduce your healing by 46%? How are you continuing to miss the point? Lets try this, you try to explain to explain what I was saying with my original point in the most good faith way possible. This is a good test to see if you are understanding what I'm saying. I don't think you do.

Do you really think I believe that if an ult is stronger than a set, the ult needs to be nerfed?

Urzigurumash

Teeba_Shei wrote: »

Urzigurumash wrote: »

Teeba_Shei wrote: »

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Ok so Trees Ult needs a nerf cuz it heals so much better than Almalexias Mercy? Since when do 5 Pieces equal Ults

Does wearing Almalexias Mercy reduce your healing by 46%? How are you continuing to miss the point? Lets try this, you try to explain to explain what I was saying with my original point in the most good faith way possible. This is a good test to see if you are understanding what I'm saying. I don't think you do.

Do you really think I believe that if an ult is stronger than a set, the ult needs to be nerfed?

Isnt that what you said? Corrosive needs to be balanced against Lampknight?

Urzigurumash

Teeba_Shei wrote: »

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Right here dawg, plain as day?

Teeba_Shei

Urzigurumash wrote: »

Teeba_Shei wrote: »

Urzigurumash wrote: »

Teeba_Shei wrote: »

RealLoveBVB wrote: »

Teeba_Shei wrote: »

The developers realize how strong the penetration is. Just look at that set that gives you 100,000 penetration. That set has to reduce your damage by 46% to remain balanced. Corrosive doesn't have any damage reduction and makes you functionally invulnerable. Something feels off about that.

Well, this set looks powerful, but isn't at all.
You could also have 1 mio penetration, but there is no difference at all.
Most PvPers have around 20-35k armor.
You can easily reach this with balorgh or when building around penetration.
But 46% damage reduction makes this set totally useless.

You missed my point entirely. The set would be completely overtuned without the damage reduction. Corrosive doesn't have that damage reduction, thus its overtuned. You actually agree with me.

Ok so Trees Ult needs a nerf cuz it heals so much better than Almalexias Mercy? Since when do 5 Pieces equal Ults

Does wearing Almalexias Mercy reduce your healing by 46%? How are you continuing to miss the point? Lets try this, you try to explain to explain what I was saying with my original point in the most good faith way possible. This is a good test to see if you are understanding what I'm saying. I don't think you do.

Do you really think I believe that if an ult is stronger than a set, the ult needs to be nerfed?

Isnt that what you said? Corrosive needs to be balanced against Lampknight?

No you missed the point. I'll rewrite the post again for you.

It’s clear that the developers understand how powerful penetration is in this game—just look at the design of the Lamp Knight set. It grants an enormous 100,000 penetration, but in return, your damage is reduced by 46%. That’s a massive trade-off, and it tells us something important: penetration at that scale is so impactful that they had to implement a huge damage nerf just to keep it in check.

Now, compare that to the Corrosive Dragonknight ultimate. I’m not saying it should be balanced against the Lamp Knight set, since one is an ultimate ability and the other is gear. But the contrast is interesting: Corrosive gives you effectively the same kind of full penetration—by ignoring all of your target’s resistances—but without any damage penalty. In fact, it also makes you functionally invulnerable during its duration.

This raises a fair question about consistency in design philosophy. If penetration is so powerful that one effect needs to cut your damage in half to be viable, how is it that another effect can grant full penetration and major defensive benefits with no trade-offs? Maybe it’s time to consider removing the defensive component of the ultimate to keep it within balance.

Again, it’s not about saying the two effects should be exactly equivalent—but when one is heavily penalized and the other is pure upside, it makes you wonder whether all forms of penetration are being evaluated with the same standard behind the scenes.

React

I don't know that I agree with the "ball groups will abuse it" sentiment, as I'm sure there are much better and more efficient options than spamming corrosives and gimping their ult gen.

That said, I do think corrosive should be changed to a purely offensive ult. Remove the defensive aspect entirely and buff the DOT portion substantially. If people want a defensive ult, they can take the magma shell morph.