In the Greymoor update, we got several adjustments to sets, and it appears that will be continued in U27. A dev comment in the 6.0.5 patch notes explained that the goal is for 2 piece monster sets to be balanced with 5 piece gear sets, which is an idea I agree with (typically trading off one of these for the other in builds). I would like to comment on the current form of Grundwulf and explain why it is not currently balanced, and has fallen out of use.

In its current form, Grundwulf gives a maximum of 700 primary resource and 350 secondary resource every 5s. This results in Grundwulf returning 140 primary resource per second and 70 secondary resource per second in the best case scenario (crit to proc it exactly every 5s, and no downtime in combat).

First I want to look at what values a typical sustain set should give. I'll look at this from a magicka point of view for simplicity, but all the same points can be made from the stamina perspective. We can see from comparing the Atronach and Apprentice mundus stones that Magicka Recovery and Spell Damage are valued at a 1:1 ratio. This is confirmed by jewelry enchants, which give either 169 Magicka Recovery or 174 Spell Damage (not quite 1:1, but 97% is close enough for this discussion). With this conversion, we can use the golden standard set: Julianos. While it is fine for some sets to be more powerful than Julianos (especially if they have a special condition for use, or are difficult to obtain), historically any set that is weaker than the crafted Julianos has ended up unused (may as well not exist in the game).

So converting 300 Spell Damage to 300 Magicka Recovery we get a good baseline at what a Recovery set should be. Typically a build will have bonuses to Magicka Recovery through Evocation (20% to 28%), Arcanist CP (14%), Major Intellect (20%) and Magicka Controller (2% to 4% depending on Mage's Guild skills slotted), resulting in approximately a 1.6 multiplier on Magicka Recovery. Note this could be significantly higher if you include Minor Intellect (10%), Magicka Aid (10%), and Capacitor (10%) or Flourish (12%), in some cases nearing a 2.0 multiplier. To be conservative with this, and representative of a reasonable worst-case, I'll stick with the 1.6 multiplier and say that 300 Magicka Recovery gets buffed to 480, which ticks every 2s for a total of 240 Magicka per second as our baseline value.

Now let's bring in some additional examples to see if this 240 Mag/s is a reasonable baseline.

Amberplasm: Currently gives 276 Magicka and Stamina Recovery. The Magicka Recovery gets the 1.6 multiplier, but the Stamina side has no guarantee of bonuses on a Magicka build, so to be safe we can assume a return of 276 x 1.6 / 2 = 221 Magicka per second and 138 Stamina per second. Note the Magicka return is slightly lower than the baseline 240/s, but it also has the additional utility benefit of some stamina return as well. I believe this is fairly balanced.

Previous Amberplasm: Before Greymoor this set gave 250 Magicka and Stamina Recovery, which resulted in 200 Mag/s and 125 Stam/s. In my opinion this is also reasonably balanced with the baseline 240 Mag/s. I have no problem with the slight buff in Greymoor, but it's interesting to note that the balance team found this to be slightly too weak.

Shroud of the Lich: This one has a proc condition, so is a little tougher to compare, but at max uptime (20s every 60s) it gives and average of (1032 x 1.6 x 20) / (60 x 2) = 275 Mag/s. This is higher than the baseline, but given it's proc condition I think this is reasonable and balanced.

Vestments of the Warlock: Again, a proc condition requiring low magicka, but we can look at the maximum potential of 11350 Magicka returned every 45s or 252 Mag/s. Maybe a little low compared to Lich, but this one at least exceeds the baseline 240 Mag/s to account for its proc condition, and seems relatively balanced.

Bloodthorn's Touch: This set isn't very well-known, most likely because it has been underpowered since it's introduction. It gives 660 Magicka and Stamina on direct damage with a 5s cooldown, resulting in 132 Mag/s and 132 Stam/s in a best-case scenario. Strangely, this seems to be the set that Grundwulf was adjusted to match (although Grundwulf is actually significantly weaker than Bloodthorn on the secondary resource), but I believe Bloodthorn is an outlier and not balanced with the rest of the game.

Original Grundwulf: As released in Scalebreaker, and in Dragonhold and Harrowstorm, Grundwulf gave 1000 Magicka and 500 Stamina every 5s, resulting in 200 Mag/s and 100 Stam/s. This is fairly close to the baseline values, and extremely similar to the old Amberplasm (only missing a little secondary resource sustain). Even if it had been untouched in Greymoor, Grundwulf would still fall behind the new and improved Amberplasm.

TLDR: Grundwulf did not need it's resource return decreased in Greymoor, the original values were much closer to balanced with most other sets in the game. If anything it should have been increased to 1100 Primary and 700 Secondary resource every 5s to match the new standard set by Amberplasm. Bloodthorn is not a good example for comparison because it is also in need of a significant buff (yet still somehow outperforming Grundwulf currently).

@ZOS_GinaBruno @ZOS_Gilliam @ZOS_RichLambert thanks for reading and considering.