Normally I believe the idea of AST was to not really be a "better" healer by using certain stance, but being able to "fill" what is missing, depending on whether you have WHM or SCH in your team. And replacing one or another doesn't mean you have to be as good as them - that's why SE gave AST some cards. And cards feel just not good enough.. There's a lot of playing with cards, shuffling, drawing thinking on who to use, but after all that they just feel not that good for how random they are.
As for damage i dont think AST was intended to deal some damage. Until lvl 54~ AST has very poor damage abilities, and soloing would be horror.
So here's how i see it: AST fills the role of a second healer. And is not better than the healer that is being "replaced", but AST has something unique - cards, to benefit the team for what's missing. And well currently cards are a bit too complicated with spread only possible in combat, long cooldown on shuffle, etc.