SE did a good job at addressing AST's faults in terms of its healing potency on skills and the problems with its CDs like Lightspeed. The problems that still plague AST come from its card mechanics that suffer due to rng and fiddling with trying to get the best possible outcome with the cards you get during fights. The rng can completely screw you over and cause your value as a healer/support to become lower than WHM/SCH. During dungeons this isnt a big deal but on difficult 8 man encounters the skill cap for AST shoots through the roof compared to easier instanced content while your trying to weave cards into healing.
My advice to SE would be to change it so that AST can focus on healing during encounters more by making the cards permanent buffs. Obviously there would need to be changes to the potency of individual cards and there would need to be a cap on how many cards you can put out but redesigning a mechanic based on 4 skills is easier than redesigning an entire class.
I imagine it would look like this
Draw = same
Spread = Add the currently drawn card to your spread. You can permanently affix the card to a party member that stays until you die. Max cards in spread: 3
Royal Road = Cast on a party member that is under the effect of a card in your spread. The effect is based on which card they are under. CD = 300 seconds.
Bole/Balance: 400% potency for 10 seconds
Arrow/Spear: Gain The Arrow if under The Spear and The Spear if under The Arrow for 15 seconds. This affects all party members under either card.
Ewer/Spire: Spread The Ewer or The Spire to all party members for 20 seconds.
Shuffle = same but with a 10s CD.
Balance changes. The upside is they stack with all other effects that are similar.
Bole = 5% damage reduction
Balance = 5% damage increase
Arrow = 10% skill/spell speed
Spear = 10% skill/spell recharge
Ewer = 10 mp refresh
Spire = 10 tp per second