While it's true they are in a tricky position, I'm not sure how you're supposed to "cooperate" with each other with AST in the group. At most, I see that as meaning you'll have to spend more time healing (to make up for the difference) and managing mana, while AST flips through cards and hopefully pulls an Ewer to help you out on MP. AST lacks heavily on burst healing capability and on-demand utility; something both WHM and SCH bring to the table, respectively.

I see working alongside AST to be more trouble than it's worth and less reliable, so far. I'm just not seeing AST as equal in value to what a WHM or SCH brings to the table, especially when all fights are heavily scripted and patterned. SCH will always have Sacred Soil, Fey Wind, etc. AST will never be able to rely on pulling the proper card combinations at the right time.