If I recall, AST is the flexible healer, it has two stances and can easily become the main healer with Scholar in a party, and become support healer with a White Mage in a party. The card buffs is just icing on the cake, cherry on top - since you cannot rely on this - they are too random, too few and far in between, and the effect is just marginal - it's not bad, but it is not great by any chance either. As it is now, ASTRO cannot heal worth a damn when shit hit the fan, two astro would pretty much spells DOOM in alliance, compare to two WHMs, two SCH, or WHM + SCH combo.
What they really need to change is the stance, make Diurnal is the healer stance, 10% more heal, and adding regen effects. Nocturnal is the shield stance, 5% faster action, shield absorb 25% damage dealt based on user's HP. On top of that they need to make essential dignity on 20 seconds cool down. Helios cure potency should be 350, Aspected Helios should be 250. Collective Unconscious also need to be changed.
Astro buffs is really pitiful, and on a very long cooldown, it's a bonus really - as it is now. If they want to keep the healing potency the same for now, then the BUFFS has to go up, on a faster CD timer. This way you can put AST as the buffer to go with some decent healing capability and will always act as second rate healer to WHM and SCH but with far better buffing that is unmatched by any other jobs. As of now, why would I want a weak buffs based on random chance, or a decent one with royal road assuming you draw a good card. SCH give a much more better buffs, that you can control.
WHM - unmatched healing potential, the best AOE healer in the game, with good damage potential
SCH - damage mitigation, constant steady buffs, and good damage over time.
AST should be - support heal to complement the other two healer classes, with unmatched party buffing potential that is far better than bard, machinist, scholar, or any other classes.