Another though I have had today while thinking this over. Why not make the AST a true hybrid? Where cards can not only be cast on party members but maybe done on enemies for debuffs or damage. This could be as simple as an inverse, such as bole and balance increasing damage taken by target, to maybe direct damage such as Ewer and Spire giving dots and spear and arrow doing direct damage. Not only would this give more reason for the AST to have the weakest attack of the healers, but would also make the card system far more dynamic in choosing between buffing your team or debuffing/attacking the enemies.

Just a thought.