AST is "similar" to Bard/MCH IMHO,

These 2's maximum DPS potential is mathematically lesser than other DPS classes.
These 2 bring precious utility to the group in form of Mana Regen/TP Regen.
You got 3 other DPS to cover up a bard/MCH's lower DPS.

Now ASTs:
AST Healing Throughput is lower than other Healer classes.
AST brings........not that great utility to the group as of Patch 3.01.
You better hope your Co-Healer's great, cause he/she's the only 1 that'll be covering you.

I think the mentality when SE was designing AST is they wanna make a support type like Bard/MCH, but didn't take into account that Bard/MCH has 3 other players to back up its short-comings, unfortunately AST only has one.