The primary issue with AST, I feel, is that it simply does not possess the synergy with itself that the other classes boast. Scholar is supported by ancillary mitigation, for example, that makes their shields more potent, while WHM is able to sustain cheaper heals through regen and freecure.

So, rather than trying (and failing) to be either a Scholar or a White Mage, I think it'd be really cool if AST took the whole concept of "Healer B" and ran with it. Made them focused on augmenting the abilities of the other healer and less for compensating inadequately for what they don't have.

Something like changing Aspected benefic/helios to a healing potency increase/percentage-based damage reduction would be an interesting way to support either SCH or WHM while maintaining some uniqueness to the class. Or letting Time Dilation affect E4E or Regen. Personally I think that'd be much more satisfying than simply filling in whatever your group doesn't have for its second healer.