All Healer jobs use an entirely different role expression to Tanking or DPS, making them feel disjointed.
Healing, however, is largely expressed through GCD healing (that is never actually used in higher levels of play), and all of them have a near-identical, static GCD rotation - Press Dia/Bio/E. Dosis/Combust, then press Glare/Broil/Dosis/Malefic 11-12 times, repeat ad mortem.
Healing becomes less complex the better you are at it.
Compared to learning Tank or DPS jobs, where the experience starts simple and you gradually learn to utilize more of your kit in interesting ways, the peak of complexity for healing jobs is at level 4. As you learn to use your kit, the base experience actually becomes less complex and less interesting
Healers are unnecessary.
Encounter design in this game is very rigid with almost no unpredictable damage spikes.
Original point:
The current state of healers is outright unplayable. I cannot convince anyone I know to play them. They are so incredibly mind-numbingly painful to play that finding someone who both has sufficient experience with the role to be capable of clearing the content, and does not outright refuse to play the role, is impossible.
Just remove healers and give Tanks/DPS enough defensive tools to manage without in Extreme and harder content. Stop making us suffer.