With AST had dozens of issues, but still with only an occasional wipe(before the 3.05 AST buffs).
With SCH never really had issue and never wiped when leveled all my way through the vault.

The problems starts coming when people don't avoid aoes, and are getting bleeding debuff, if they get it, it just takes way long time of GCD to dispell and reheal it before another room wide AoE strikes.

As for a SCH what i was doing: Use Eos, place her in the middle so that she doesn't have to be running around and wasting time not using embrace by following you. It doesn't matter if she's on obey or sic much, she does fine there on auto. Holy flames are rather easy to kill, you can kill 2 of them in cleric stance.
For the last phase.. try to have 3 lustrates up, and just do basic heal/adlo thing as regular.

it's challenging for a healer, but it becomes nightmare only when people don't avoid avoidable things.