The irony with the Vault is that it requires healers to be a bit more on the ball and I'd say 60% of the times I go into the vault as DPS or Tank, our healer struggles so much. And I guess becauase many healers are so used to a much more relaxed pase of healing and being able to idle a lot, when actually more intense healing comes up, it's too much for them.
While this fight does require all party members to be on the ball mechanics wise. I've seen tanks and DPS exact the fight perfectly and the healer struggle to keep healing up during AOE dmg or tank taking dmg.
I've never had issue DPSing as a healer in that fight and find the damage coming out pretty fun to deal with - but not so much that limits me to a heal only role. Even with messy tanks and DPS.
