The only problem is that is the RNG nature of the buffs offsets the healing power, if they were to remove the RNG nature, the job would become too powerful since it can full heal and buff at will. My guess is that they are going to keep the current level of RNG and just alter the effects of the cards, extend the duration, or enhance the existing effect.

If they buff shielding, AST would easily replace SCH in almost every aspect of the game. If they buff healing, AST would replace WHM in almost every aspect of the game. The only changes they can make that would still be fair to the other 2 healers is in the card system.