If SE wants AST to be viable in the hardest content, the randomness of the class has to be removed. Even though the lore that surrounds AST is amazing and the random nature of the cards are supposed to be the base of the class, until we get rid of it there won't be a reason to bring a AST over SCH/WHM due to our unreliability. Healing potency is easily adjustable, but when end game mechanics requiere to use specific set of abilities in a specific moments, the random nature of the class united to the weak effects of the cards in overall make AST not desirable if you want to progress through the end game in the most efective way.