Healer problems are easily solved by giving problems to players that can't be solved by just adding more tanks.

More punishing mechanics need to become a regular mechanic that is added in at some point during fights.
- Kefka-like Doom Raidwides: everyone's HP is dropped to 1. Also get a doom debuff that is cleansed when reaching full HP. If not full HP at the end of the debuff timer, you die. Goes through invulnerability, of course. Can make non-lethal variants of this debuff for normal content, but the resulting consequence should be enough that it's just always preferable to have a healer.
- Throttle debuffs on all non-healers. Must be cleansed with Esuna. If not cleansed, you die.
- Powerful bleeds and armor-reduction debuffs, all solved by having a healer output some more healing.

Then you can do a gamewide patch:
- All tank and dps skills and abilities that provide healing or shielding is changed into some form of damage reduction for themselves, or a self-buff to increase damage. They can take a beating, but they can't survive forever.
Let healers heal and be the ONLY source of healing. Just like tanks are the only role able to survive tankbusters reliably and/or use invulnerabilities. Healing should be a unique trait that is only done by healers.
- Automatic self-healing is removed entirely in extremes, savages, and ultimates.


There, now you made healers more in demand.
The weaklings will complain that "omg but this means a bad healer can ruin the whole party "... and yes.... so what? A bad DPS will never let the party clear. A bad tank will let themselves die, then their co-tank, and then the whole party. Stop coddling healers. Give this class the power fantasy it deserves.