Tank most likely stood in stupid or didn't block/interrupt special attacks that is mandatory. DPS should be able to dodge or block in case aggro is lost for a second. Scaling is not good and if you are underleveled even with scaling you will be at a severe disadvantage the biggest issue being sustain.

I do not find any of the 4 man content minus White gold tower and Imperial City Prison to be that difficult if the people you are running with are at least some what knowledgeable of the dungeon you are running.

There could be something to say about the last boss on City of Ash but as long as the group understands the fight and no one is a vampire it is really not an issue.

I will agree if you are now a Champ 160 character and you are running Champ 10 gear you will get hit pretty hard in these dungeons.

Some fights will get overwhelming if the DPS isn't there. Ex: Banished Cells - my tank is well-geared, but if it's taking 5 minutes to whittle the boss down (forget about dealing with the Daedroth) to half health, I'm going to start feeling the resource drain real bad. Meanwhile, if it's taking 2-3 minutes to get him to 30%, I have much better odds of not running out of resources. Other examples include the wraiths in vCOH and Horvantud's adds in vCOA.

Other than that, it's pretty much a power creep for characters who have graduated from normal to vet content. Normal content usually hits like a soft pillow except for one painfully telegraphed attack (e.g. a cleave). Vet content can sneak up behind you like a... sneaky thing. I like to think I'm good but sometimes by the time I realize Gamyne Bandu in vFG has put those health-sapping balls on me, I'm already dead. You kinda need to be on your toes for most of the better-designed vet dungeons.

I find that it's easiest to deal with vet content on healers, though, if that helps! If the DPS is good and the tank is decent, you ideally won't be needing to heal much and can help with DPS or buffs. This is assuming your DPS doesn't stand in stupid, your tank holds aggro/faces the boss away from everyone if they have an AOE, etc..

The problem with the vet dungeons, is non-experienced players not understanding the mechanics of boss fights. I did vFG twice yesterday 1st time w my stam NB dps, we did speedrun (under 20 min) with 1 inexperienced player (a stam temp dps). Only deaths was when we wiped on last boss because said inexperienced player entered bubble voiding gold key run. (we then explained that mechanic to him and 2nd attempt was no problem) We did that run with 3 dps and healer no tank. 2nd run was with my magicka temp healer, that run did not go as well, both dps were inexperienced, and it took us cycling through 3 tanks and better part of 2 hrs, to get 1 who had the patience to get us through for the gold key, and I went through around 40 mag. potions healing them.

The 2nd biggest problem IMHO is players who although they might have the experience and knowledge to complete the dungeon, do not take into account the group that they are in. Tanks that want to 'Leeroy Jenkins' their way through, and dps that spend half the dungeon posting their dps #'s and berating other players for their damage output are a few examples. They very often are the 1st to quit the group when something goes wrong.

With the exception of the IC dungeons (WGT and ICP) all the dungeons vet and norm can be run without a tank and in some cases can be run 4 dps if the group understands the fights. I am very patient, and never quit groups. I have done many training runs on the vet dungeons with 3 inexperienced players before for gold keys on many of them, what makes the difference is for someone to step up and take the time to clearly explain the fights and/or give advice on skill choices/tactics. This usually only takes a few min. Most dungeons I can tell after 1st or 2nd boss fight if some1 in group does not understand mechanics, and then I will ask if everyone knows the fights pointing out that I will explain them if they do not. I play all 4 classes, all 3 roles, and have done all the 4-man dungeons, so I have a pretty good idea about how the game works.

I rarely run dungeons with guildies and occasionally run with friends. The overwhelming majority of runs I do are in pugs. I find that the majority of groups I am in. The majority of groups I am in run the content with a minimal amount of difficulty completing it. There are only a few fights (outside of WGT and ICO) where a tank can make a difference for an unknowledgeable group. Group dungeons in this game really come down to dps output. The faster and more efficient your dps players are the fewer boss mechanics the group has to deal with.

As far as your groups getting wiped. Without knowing the specifics of the scenarios, I can tell you, most of the time when dps players die, it is their own fault, not the healer. They not only need to know how to deal damage effectively but also how to avoid/mitigate/dodge/block/heal through the fights. If your tank was using his health it was probably his fault as well. They need to understand the mechanics and have a build to get through the content. tanks can not simply rely an the healer to continually heal them, they need to use the appropriate combination of skills and tactics to take some pressure off of you. If you are constantly healing because your group can not stay alive, you will quickly run out of resources keeping them alive. You definitely want to upgrade your gear but TBH it's more about understanding the fights.

The no.1 problem as a healer is when ppl get out of range for your heals and second is that you need to be able to stay alive yourself to keep healing up, meaning that you will need to dodge, move out of danger/reposition, block/interrupt during fight which all will make it impossible to be healing continuously.
Your group need to have some kind of self healing and not completely lay the burden on you as a healer. The third problem is that with all changes that came with DB was also that cost for magic/stamina have been changed for each skills which also make it harder to maintain resource management.

As Templar you have access to Luminous Shards as an example which will return both stamina and magic to player if those will be fast enough to activate it during a fight. It does also a short disorient for 6 seconds (CC) [time which DD can do more damage or when DoTs can make their work or when HoTs can heal up from Rapid regeneration from Resto] and is an AoE damage. Repentance is another very useful skill which both heals and helps with returning some stamina, even magic based build needs stamina to dodge, block or break free. Cost of those skill have also been increased, so all together it have been more changes then just replacement of Veteran Rank to Champion Points.

The best healer isn't a "pure" healer, but someone that adds debuffs, provide some kind of CC or help with damage like Elemental Drain, Purifying Light or Radiant Glory all which either return magic or heals at the same time.

Destro staffs and Resto staffs passives and some CP in Staff Expert will also help in returning magic for your pool of magic again with heavy/light attack.