Has anyone quit healing?

[Renathras]

Yes the game was built like that

The game wasn't. That's kind of the point.

As for Toxicon - they could both be GCDs and it would be a combo/interaction system though, yes? Just with a lower APM.

(nobody has ever been one)

...okay, when did you join the game? BOTH WHM and SCH were GCD healers in ARR. WHM (and I think dAST and possibly nAST, but I didn't dabble with them at the time) were in HW. WHM was in SB. WHM was in ShB. WHM is in EW. WHM has never had enough oGCDs to heal high end content effectively via their use alone. Lilies are GCDs, and a goodly chunk of WHM's healing. The top WHM I found on the Abacus fr P5S did ~38% of his/her healing with Rapture. And presumably that's a player that has learned to minimize unneeded healing. P8S-2 is interesting, in the top team and top WHM (WHM/SGE comp) did 25% with Rapture...and 20.5% + 8.5% with Medica 2 and its HoT, oh, and 1% with Regen, a GCD, for a total of 55% of his/her total healing with GCD heals.

CLEARLY some Healers - including top teams - have been GCD Healers. WHM has never not functioned on a GCD healing paradigm, and SCH and AST did in the past). I get sticking to your guns, but you have to admit that your absolutionist position isn't correct. If you said "Several have not been", you would right, though. SCH has had a heavy oGCD focus since HW, and probably since late ARR, and AST since SB, and SGE its entire existence.

...but that's how they've been feeling for 2+ expansions,...

Not ALL of them. That's my point. As for Deep Dungeon; from what I understand several aren't terrible, they just take some thought. AST is the worst in the game for DD though, apparently. Low personal DPS (WHM and SGE have higher), no passive healing (SCH and SGE have), and its buffs don't boost its own damage enough. Doable, people have done it, but the least desirable. This is why WHM and SGE are considered functional at it, SCH meh, and AST pretty terrible: https://www.youtube.com/watch?v=Ab-zwGUL__0

...but when talking about solo content, people are talking about MSQ and solo instances, not DD.

Surely the fact that SCH was super DPS heavy in ARR, while WHM was left to 'healbot' in stuff like First/Second coils (Final was where people started DPSing a lot more I think), proves that 'healers should DPS' WAS always the accepted paradigm the community ran by?

Couple things here:

We're talking about the Dev design intentions at the outset of 2.0, not the community standard. Moreover, WHM being "healbot" would prove that "Healers should DPS" was not the paradigm. If it was, there'd be no "healbot". WHM and SCH would both have been going balls to the wall DPS, which wasn't the case. This indicates, at best, the community paradigm was that SCHOLAR should DPS/support heal while WHITE MAGE should be a strict healer. Basically, it means more or less the opposite of your take, and at best, means a nuanced hybrid of it, which I've presented before.

But that wasn't the community standard until late in ARR, not in 2.0. Moreover, it wasn't the Dev design intent based on how encounters ran (no tight Enrages, no required Healer damage), a position they went on the record with in HW (even if it didn't fit the actual encounters).

And given that groups were doing things like three healer WHM/WHM/SCH runs, it's not at all clear "optimizing damage" was the accepted community standard at the time. The push for "more DPS" didn't get stronger in casual content. It was actually a huge point of contention that it was being pushed by a small segment of the community, so much so Cleric was eventually removed entirely.

I started in 2.3 and I never heard that healers were "supposed to DPS" or "how different healing was in FFXIV" until mid-HW. That's when people were actually talking about it across the community. Before then, it seems to have been a somewhat niche conversation among the raid community that no one else was in on. Now, I personally used DPS spells if my MP allowed for it and healing wasn't needing to be done (unless MP is tight, I've never been a fan of taking no actions, which is also why I thought WoW doing the "healer damage spam spell costs no mana" was such a great move, since you could fill dead time with it without compromising your healing - something FFXIV did NOT do, which is what you would do if you were designing a game for Healers to do damage...). I even remember running a dungeon lateish in HW as a PLD (leveling my 4th and last Job I'd get to 60 before SB came out) and running into a dungeon with a SCH, SMN, and BRD, and none of then knew what DoTs were. The SCH didn't cast any DPS spells or enter Cleric. Of course, back then, people actually talked in dungeons. They said they were new, so I went super gentle. I also explained to the SMN and BRD how their DoTs worked (and I had ARCher at like level 20 at the time, so my knowledge was limited; I did have WHM, SCH, and SMN at 60 though), and to the SCH that they could use Bio without needing to cast or go into Cleric and they could plop down Shadow Flare and I would drag the enemies into it. ...got 3 comms for that run and some thank yous. But the point is, it was hardly universal in the community that this was "the way to play".

Yeh, and of the three solutions,...

Debatable. Again, the status quo is widely accepted by the bulk of the community, and it's not at all clear what such a change would have. You also don't understand the premise. Me saying change 3 and leave 1 isn't an agreement that the current design is flawed. It's me believing that some people aren't satisfied with the current design and an attempt to appeal to them while also appealing to the people who are satisfied with the current design - in other words, to please everyone.

The alternative is to change none of them - not to change all of them. You mistake what the alternative/status quo is.