For starters to fix Healers, their attacks need an increase in potency. Their base damage output should be on the same level as tanks... Or alternatively they could nerf tanks to Healer levels of DPS... At this point of neglect towards the role, I would welcome the chaos caused by that.

Also, give them more of a supporting role in the group. Healing is usually only specifically needed when someone fails to dodge a mechanic, if it doesn't just straight up instakill them... Otherwise regen and Kardia/Eos is enough to more or less keep tanks alive, and most raidwides only need like 1 casted AoE heal to recover...
But for other kinds of support, there's only really Buffs for the raid and debuffs to enemies...