I tried to play AST in savage content and I've managed to clear E2S, currently working on Levi prog at the moment. I have to say the new card system is just bad, it's really a clunky mess to use. After a while, I began to realize that it's incredibly difficult to weave cards in between GCDs, this is partially due to having to constantly select who to give the card to, something that wasn't as much of a problem in SB. This is compounded by the fact that fishing for a seal can be a huge pain in the butt. In the worst-case scenario when fishing for a seal you end up drawing a card, re-drawing 3 times, using minor arcana to burn the card, and throwing it out to a DPS; That's 6 oGCDs which doesn't even amount to a seal. For simplicities sake, say that an average GCD is 2.5s, that means that you spend 15 seconds just trying to get a card out, assuming you don't use lightspeed. Then you have Sleeve Draw on top of that, which fills up at the very least 4 oGCDS and at the worst 7 oGCDs. I realize that these represent the worst-case scenario, but no class, particularly a healing class that relies on oGCDs to heal, should have to spend 15 seconds to get a buff out.
Overall, ASTs are functionally viable on paper, logs have shown us that the rDPS is slightly below an SCH, but they have an overall higher healing output than WHM and SCH. However, it functionally has a lot of problems with its core mechanic and it's MP management. The MP management is somewhat easy to resolve for SE, since they could easily attach it onto an existing skill. However, the card system is just a mess and needs a rework, it's difficult to achieve proper optimization with the class due to the way the card mechanic functions. That being said my complaint in this post doesn't even address some of the problems I and other people have with the cards which lie in its simplistic nature.
I plan on switching to SCH next week, it's no longer worth the headache to deal with cards and somehow get my oGCDs out. I really don't understand how anyone could like the current system, particularly based on how clunky the card system is, but this thread has shown that some people like it for some reason. I'm really disappointed with SE, AST use to be one of my favorite classes to use, but I can't play it in its current state.