This is only an issue with games that heavily punish you for dying.
In another game I played the damage was very heavy people died a lot but the only real punishment was a slight loss in dps and sometimes resources.
Healers managed debuffs, buffs, health, mana, and even death. Contrary to popular belief death isn't a bad thing unless the developers make it work against you.
Death was so common you specialized your revive skill so it could be used faster, took less mana, and revived said person with full hp and mana.
None of this was a large issue because of the way they dealt with enrage.
Enrage wasn't just some timer where you all die at once, enrage was literally that, the boss went berserk.
The boss's actions would become so fast it would clip their animations, their damage would increase and this process would continue until everyone was dead or the boss was defeated.
They also had consistent inconsistent damage (E.G. 5-20 seconds of straight damage to someone or the party where if left alone for 5-10 seconds said person would die) across the board.
Most damage you were able to dodge in fact it was rare to ever see a mechanic you couldn't dodge if good enough and that's how they kept healers balanced.
The base level required healers, as you got better and did harder content healers were even more required, even as you got so good you avoided all damage healers were still needed because they needed to give you mana and cleanse debuffs on you and buffs on the boss, sometimes you would even need to heal yourself to grab aggro of mobs to kite.
This careful balance between the skill floor and the skill ceiling and understanding that the game is punishing while alive but doesn't punish you much for dying is how healing was kept relevant across all levels.
What I just described weren't even the mechanics of the bosses/mobs but simply what the basic healing experience was across the board regardless of what choices you made in specs or class.
The fact healing isn't engaging in FFXIV is entirely a self inflicted wound created because of YoshiP's obsession with total and absolute inclusion.