As they state in their liveletter they are aware of the overpowering factor for AST buff
Because they want to push the whole AST pool up disregarding the fact that Top-chart AST will automatically skyrocket

As an AST fanatic I'm far not opposed to that, especially because since AST creation I'm fighting the fake WHM supremacy as top healer
But now I also feel that it was far too much left away, and that WHM really lack fun compare to the other healer

I mean AST got same power of healing, less enmity, less mana cost and far much more group utility

WHM in the opposite got strong firepower for a short time which is perfect for dungeon, less for Raid (not impossible, just not funny to manage)