I don't think they'll raise the potency of Benefic without also raising its mana cost.

@L60, Benefic cost 353 mana, for its 380 potency heal (0.92 mana-per-potency), while cure is 442 mana for its 400 potency (1.1 mana per potency). so in actually, Benefic is more efficient. Its just less potential throughput, but its alot cheaper for what you get.
I think that for what it is, a low-cost, spammable heal, benefic is great.

What AST needs, is burst capabilities.
WHM gets burst healing in the form of divine seal and presence of mind.
SCH gets burst healing from Eos (Fey Covenant), burning aetherflow stacks with lustrate or indominability, regen from Eos as well (which is very strong when paired with rouse and Illumination, so I view it as a cooldown), but also gets mitigation to make the healing required less: Sacred Soil/Shadow Flare, Fey Covenant.
All casters except AST get access to virus and eye for an eye.

What AST gets, is a long cooldown Essential Dignity, and a Benefic2 proc, both of which are only good for a situation in which you'd use a lustrate: a single damage spike. Those don't fill the role of burst healing for 20s to compensate for a large pull, or debuff on a tank, or similar situation. All an AST has for that, is if they're lucky enough to have an Arrow card to use on themself for extra speed. I've taken to saving spread for Arrow just for myself if I know that such a time is coming.

I had forgotten about the card stacking problem, and I agree completely. Cards need to not overwrite each other. I'd go so far as to say I'd like to put two cards on the same person by spreading one first, drawing another and playing them both on one person.
Being able to more reliably get good cards would go a long way to making that useful. Part of that, I think, is that most of the cards aren't that useful. Rather than skipping the "Bad" cards, I'd rather see all the cards "good" in more situations.
Make Bole abit stronger, perhaps by adding a healing received buff to it in addition to mitigation, or a regen effect. (this could be good for Nocturnal Sect AST to have access to a regen, similar to how SCH have access to one.
Spire and Ewer both do the same type of thing, but only apply to one type of class or another. they should be merged.
Also, could probably do another card that provided mana/tp recovery, instead of cost reduction. This would make both cards useful to anyone.
Spear is strong, but very difficult to coordinate. Perhaps it should apply to cooldowns that are in use in addition to ones that are activated during its window. For ones that are in use, I'd only expect it to affect the remaining time, so that its better to use it around then time that cooldowns are activated, rather than being completely useless when it lands right after activation.
Balance is good, and Arrow is good. Neither one is a waste.

I do agree, that a healing potency cooldown needs to be part of an AST toolkit, they're an essential part of WHM and SCH burst heals. Perhaps a cooldown that gave Nocturnal Sect a burst of speed, or Durinel Sect a burst of potency. A little yin to go with the yang, so to speak.