Problem is, the formula already has been changed, without consideration or regard for what players previously wanted.
The appeal of doing dps as tanks and healers in Heavensward came down to carry potential. Your WAR showed up in full STR gear (or some crafted, if they wanted to play a bit less greedy). They had marginally more HP than your Dragoon. They then turned out to be tankier than your PLD, while doing more damage than your BRD. Your SCH spent pretty much the entire fight in Cleric Stance, but they're also still managed to somehow solo heal your team when your WHM died. These were your carry heroes. It felt good to translate your mastery of a role into a gamechanging advantage for your team.
From Stormblood to Shadowbringers, we've seen a progressive effort from the dev team to separate out the dps done by 'true damage dealers' and the rest of us. They've done this by placing restrictions on our gear and limitations on our stat progression (and even our access to certain procs, like DH). In some cases, they failed spectacularly and embarrassingly had to backpedal (see: i270 strength gear in Stormblood).
But the devs don't want what you want. Even if you're the 'best' healer player, your damage by default is going to be a fraction of a player who picked DPS, irrespective of their competence. This is only going to get worse with subsequent expansions. Can't have you embarrassing your DPS for binding all their keys to auto-attack, now can we? And if doing damage is the only thing that has value, then where does that leave you? Is there any surprise that people now want to switch off these roles to DPS?
As a healer, what do you have to offer your team, besides being a half-strength dps? Under such conditions, if healing has no impact, then healers have no impact.
I don't think this is universal. In Stormblood, there were a couple of influential streamers who argued that Crit/DH procs were unfair on WARs trying to achieve their perfect dps run. This is obviously dumb, because the entire point of having Crits is to introduce in some variability in your damage output. What was baffling was that the dev team actually listened to this suggestion and made everything into guaranteed Crit/DH procs.
I mean, we can suggest more dumb things out of our own convenience. Any healing requirements in a fight detracts from our ability to maximise our dps. So we should get rid of HP and heals altogether. The only way you can now die is by failing dps checks or by messing up mechanics. Actually, better yet, actually playing the game is difficult. They should just replace fights with animated cutscenes of the players winning and collecting gacha Mogstation glamours. There, even less variability.
You can't blame the average layperson for suggesting ideas that they haven't thought through properly. You can certainly blame the dev team for catering to dumb suggestions, though. There's a problem with being too polite.
Either approach is fine. But you have to remember: the average player picks DPS. It's that single player game mentality. People pick tank and healer specifically because they want to make a difference to their group. If you neuter the impact that these roles have (because wipes make people feel bad), nobody will play them.