Yes, WHM is the most potent DPS out of the three healing classes, while AST I believe is the weakest.

AST's power is mostly tied to their cards, any DPS increase to party/raid members could technically be considered to be your damage.

An AST is definitely a good choice for dungeons and raids if played well, but soloing anything sucks, unfortunately. Par for the course for SE's tendency to only care about raid data when balancing classes.