Lols.

Sounds like that SCH is mis-informed or he and the tank were on TS.
There is no way, you should be able to pull unless 1. DPS is bad, 2. People are undergeared so you are healing too much or 3. the tank has no idea how to keep threat.

FPE: I can use cure 3 and medica nearly every 6 seconds is I wanted lol.

On huge aoe damage throw on cure 3 when everyone is bundle, and top up if necessary with a medica. On timults you should be working with another healer and interlocked casts of AOE heals should not produce much threat, (out of curiosity how much does your SCHs succor do ?) You can cast medica twice during this and you will be fine.