The biggest factor in dungeon success will always be the competency of your party.

The game is designed so that ALL healers will go OoM if people are constantly standing in crap and getting hit all the time.

It just happens that AST goes OoM far sooner than SCH or WHM so it's more important that ASTs have good parties, which is one of the reasons they need to buff the class.

If we ASTs will be queuing as healers, then we need to be able to handle the occasional crappy party.