@OP
I disagree with turning the cards into heals. That will put AST in the same position WHM was during Stormblood. Well you did mention you keep the buffs but add an healing but that would most likely lead to overhealing. The way they seem to go with AST is basically intersecting the sects anyway so we'll see how things go in the future. However there is no content that needs that much healing. It would be pointless unless things went horribly wrong. on top of that it would lead to Diurnal AST to hold cards so they could shield at the right time while Nocturnal would overheal DPS like crazy.
Originally I believe the reason AST's dps was (is) so boring was so they could focus on the cards and buffing their team mates. Now everyone is an AST dps wise (one button spam yaaay...) except the other healers have no other mechanic to focus on.
I disagree with this. In fact ever since AST was introduced this has been its thing. Its a thing of supports in general and AST is the most supporty healer therefore you need some of this knowledge.
And no, you don't need a parser. You need to talk to people. Communication is important. If you're not willing to try other jobs to get a feel for them at least talk to the people who play them as it's another way to get knowledge.
In fact it's also knowing how other jobs work that elevate good healers to godly levels. Don't underestimate the power of knowledge.
As an example, and this is was very niche and not usually woth the trouble but even with the old cards if you knew how Summoner worked you could get them more Ruin IV casts (although it's easier to fish for balances lol) which would boost its dps. So basically you had Arrow for BLMs, Spear for BRDs and technically Ewer for SMNs although no one really used Ewer that way.
With that said roles interact differently with content:
Tanks - needs to know their kit, their burst windows, and the fight in the sense of what comes, when and how much it hurts and how to position the boss to help the party optimize their dmg. communication wise they usually work closely with healers
DPS - need to know the fight mechanics wise, how to position relative to boss so they can hurt it more and not get wrecked, how to optimize their kit to squeeze all the DPS, be it how to coordinate their own buffs and when to do things early or delay them due to boss jumping away. the most "selfish" ones because even communication wise they usually coordinate amongst themselves.
Healers- mechanics, when they come and how much it hurts, have a grasp of how much their heals can heal. usually coordinate with tanks and dps if they also have mitigation tools. However each healing job has a different approach to this.
WHM- the more reactionary healer. you want your heals to go off after the damage has been dealt (learn how to precast so they go off with minimal delay). The big oomph heal job. It's my first healer and still one of my favorite even when people hated on it during Stormblood. As a DPS main I love big heals (and I cannot lie)
SCH - you need to have more in depth knowledge of the fight since your shields need to go off before the damage hits. the only thing you want to coordinate with dps is the crit boost thingy you have. Also boss the fairy around because the fairy tends to derp. It's a love-hate relationship
AST - you need to have the mental flexibility to alternate between the WHM and SCH mindset. you should have a general idea how other jobs work or you wouldn't even know that BLM liked Arrow and BRD liked Spear back in the day. Nowadays you need to understand burst windows. Doesn't change the fact that the reward you get is horribly underwhelming for the amount of knowledge you need to have to make things work in an optimal way. Anyway it's not like you can't clear if you play suboptimally so this is more of "if you want to" instead of a must. I just use Divination on cooldown because of this.
One final example of how knowledge moves you from good to great. (My numbers might be a bit off but bear with me.)
I personally absolutely hate Holy in dungeons. Why? because I usually tank in there. So here is what happens 99% of the time I go in there and I have a WHM:
I make a massive pull. i pop Hallowed ground which is 10 second immunity. WHM walks up to the mobs and spams Holy. Holy spam stuns the mobs for 8 seconds. That means I effectively got 2 seconds out of my Hallowed Ground. This could've been avoided if the WHM looked at my buff bar and knew what Hallowed looks like. They could've waited and spamed holy after hallowed ground effictively giving me a whooping 18 seconds of taking 0 damage. Nowadays I just wait for the mobs to be stun immune... that is if they don't let me die before then.
The other reason why I hate Holy in dungeons is because it makes mobs stun immune so if there's a really nasty cleave i want to stop (because dps are dum dum and don't realize they're standing in bad) and my interrupt is on cooldown i can't do anything about it. knowledge of what mobs do would be helpful here. if you get salty over the dps blaming you... yes they did stand in bad but you made the monster immune to stun. you are both at fault.
tldr: i disagree with heals on cards and if you want to be really good you need to understand how other work via communication or trying yourself especially as an AST but such knowledge is optional.
I personally hate Holy.