Going back to Semirhage's opening post, the 'Sylphie' debates, as I remember them, were about the emphasis on healing/mitigation vs. dealing damage within the role. The primary issue, of course, is that healing checks are ultimately pass-fail, so keep experienced players engaged you either design a healing/mitigation check that is so difficult that it excludes the majority of healers, or else you provide more opportunities for skill expression through dealing damage (and more interesting damage-dealing rotations to support this).

There's always going to be a subset of players who like the idea of playing a more strictly supportive part, and that's not unique to any role group (DPS included - think of physical ranged when it brought resource management tools for the party). I think where tanks and healers diverged was that there wasn't as much of a dichotomy between doing damage and performing support actions on tanks. If you had actions which forced you to waste a GCD or spend resources in order to do mitigate, that was seen as bad game design and tanks demanded that they be removed or changed. By the end of Stormblood, there was no real dichotomy between doing damage and support on tanks, so the debates stopped. You just weren't required to sacrifice damage to mitigate more, which is the best of both worlds.

There's another issue at stake, though, and this ties in to Odinel's post. The unfortunate truth is that in order for traditional tanks and healers to bring more value, you needed those hard pass-fail checks. If you make the pass-fail check softer, then you start getting in to situations where you can get away with a solo tank or solo healer (or no healer). It makes DPS happy, because they're not held back by subpar tanking or healing. You see this design more in action MMOs, where everyone brings support actions, and you simply have some slightly more support flavored DPS. But if you want to go this route, you also have to narrow the dps gap between 'pure DPS' and supports. Right now, if you're a good player, it is to your advantage to play DPS, because that's where the carry potential is. The only way that will change is if you narrow the dps gap, and I suspect this is the direction the game will need to go.

Either way, the crux of the debate is that there are really two ways of solving this, each with their share of problems. Do you push more heavily into a traditional trinity design, where tanks and healers have harder checks and you have to funnel gear to them to be able to clear? Do you make mitigation resources scant and force your healers to carefully manage their resources or bottom out? Or do you push more heavily into an action MMO design, give everyone heals and shields, and turn tanks and healers into competitive DPS that can potentially top the charts (having been given appropriately more complex rotations, of course) while occasionally saving the group with a clutch save. Either way, if you don't give stronger players opportunities to 'carry', everyone is going to just swap off to DPS.