The problem is/was the 1/2 the card where considered worthless and the mechanics encouraged fishing for buff.

To fix "useless" cards you need to either have cards buff a role (tank, healer, dps) or buff a job or rather the attributed that effect that jobs (STR, DEX, INT, MND, Tenacity).

To fix fishing, you make the AST just play the card that comes up by removing or adding longer cooldowns on things like redraw and undraw. Just play the cards no matter what comes up. You could change sleeve draw to pull the card you want every 180s and even add an ability that would either double or half the value of the card.

The only way AST can work as an RNG / Gambler job though is if you add raid utility to SCH and WHM. Where as those jobs would be a sure thing, AST would have stronger buffs because it's not always guaranteed.