At the very least with EW summoner someone could make the argument that its popularity comes from the fact that it is the easiest caster and it has a unique playstyle when compared to red mage and black mage. Whether the playstyle is boring, easy, or lazy or not is another thing, but the other two casters play nothing like it, so it fulfilled a niche. New AST doesn't fulfill any niche anymore. It functions identically to the other healers. The differences won't be in playstyle at all. It'll just come down to a what the specific distribution of X generic healing skills are compared to the other three. Anyone saying that AST will 'play so unique!' and is 'totally different to white mage' bc you have to press an extra button before you can press the totally-not-aquaveil and totally-not-tetragrammaton buttons once a minute the either doesn't heal anything harder than a dungeon, is a troll, or is delusional.
I never cared about if AST was 'optimal damage'. Even if it was balanced such that with perfect luck and perfect draws and perfect timing on the plays with my DPS players executing their rotations flawlessly and critting a lot AST ended up being the lowest dps output healer, I'd still play it. Bc to paraphrase MisshapenChair "my reward for playing a difficult and challenging class should not be doing the most damage, it should be not being bored to tears". As long as AST was viable, even if it wasn't optimal, I'd main it. And there were points where it was like that. I played the fuck out of nocturnal ast even if it was worse than diurnal. Bc I liked it. So saying 'oh it'll be better now bc you do more damage' does not mean anything to me. I never played this class for the damage, I played it for the playstyle and how it optimized what damage it had. Pressing one dps button over and over with a bunch of meaningless ogcd heals is boring and dull to me. Fishing for one specific dps or utility card and being frustrated when i draw something that isn't helpful wasn't fun either. That's why I liked dps cards, bc they could be optimized with skill expression and were always useful.
The reason people compare it to a worse aetherflow is bc of how it functions now. Aetherflow, you press a 60s CD button and get 3 stacks of aetherflow which you can spend on healing, mitigation, or a small amount of damage if you need neither and want to burn the excess stacks. But the options you have never change. AST you will press a 60s button and get 4 skills that will alternate but likely do very similar effects. So it's effectively the same 4 skills every time, except for lord/lady which alternate flat damage and flat healing. It's more restrictive bc you don't get an option to get rid of cards you don't need and you also don't have the choice to do, say, two heal cards instead of heal and mit like scholar can. There is no decision making involved, only using it or not using it. It has as much decision making as deciding to use essential dignity or not does, and all healers have that level of decision making which is very little. There's no higher skill to it than the most basic of healer gameplay which is 'when do you press your buttons and in which order'. RNG made it so you had to react to what you were given, now we can't even do that. We know what we will have each time we draw, which defeats the point of them being cards. I feel like a fraud of a fortune teller.