Realization that I could safely quit at 6.0's completion just hit me and that sucks

[SpiralMask]

Ngl, couldn't be arsed to read the novel OP. But I don't understand why you would quit the game you played for nearly a decade cause the 10 year old story wraps up. Do you not have any trust in the devs to make up a new engaging storyline?

The question I've come to is if the storyline is engaging but the gameplay isn't worth the sub fee, why not just keep up with ethys or similar play/lore channels on yt or twitch instead?
FF14's story is great, and ms./mrs. ishikawa in particular has absolutely blown me away with the quality of her work writing for this game--the ROG 1-30 quests, the DRK quests (back when classes were allowed to have interesting class quests), the azim steppe story section in SB, basically the entirety of 5.0-5.3 shadowbringers, and so on--but when everything that isn't the cutscenes has been reduced to boring at best boring (heals) and at worst deeply depressing (blu), it doesn't particularly seem worth dealing with the drudgery just to see it.

How were the healer classes destroyed? What's destroyed? They can't heal? I really don't understand.

the easiest way to explain would be that now there is no 'reward' for healing, and you're instead actively punished for playing your class and role well.
before stormblood for example, AST and SCH had a variety of moment-to-moment decisions to make during dungeons, trials, high-end content, etc in the former's different cards and means to customize them further and the latter's selection fo DoT sources to keep on top of. they were a [thing to do] when healing wasnt required (such as when the party is experienced and doesn't eat aoes, or you've got the party topped off with a large shield or decent regens and have earned yourself some time), and being able to make use of those and further contribute to the group's success was a sign of experience/mastery both for others and for yourself as well as something interesting to do.

Now, when you heal well and have the party covered (or just have party members who just... aren't bad?) your "reward" is dead time with nothing to do.
WHM lacking any sort of downtime activity was a serious problem since their introduction in AR, as their "big heal" gimmick just creates even more dead time for them, since you dont need to devote as much time/individual actions to solve a healing problem.
Rather than addressing that issue by giving the class something unique to do, they removed what the other two could do instead (and even WHM had a few of it's non-healing actions removed with ShB's overhaul as well). Keeping WHM the same, with the same issue they've had since ARR and kneecapping the other two to bring them down into line.

that the dev team appears to be actively avoiding so much as mentioning healers in live letters--for example, we had one in which NIN got two slides to explain it's upcoming rework, MNK gets a couple slides to say it's getting a two-phase rework, DRG got a slide saying it was pretty much okay and wasn't changing outside of some numbers, and healers as a whole got a single line at the bottom of an "and other changes" slide. this was the first mention of basically anything healer-related in almost a year by that point--is a separate issue that's also made more than a few people feel underappreciated or ignored.