Edit: Going to pull in some points from later in the thread for the benefit of those reading for the first time.
There is no dedicated designer on the job design team for the Healing role.
There are only four people on the battle systems team (which job design falls under). None of them prioritize any of the individual jobs in the Healer role, nor the Healer role itself as a whole.
All Healer jobs use an entirely different role expression to Tanking or DPS, making them feel disjointed.
The design of Tanking jobs is largely done through a constant and largely varied GCD rotation that has little (or only passive) impact on their mitigation. Their role expression is done through OGCD abilities that do not affect the flow of the job in any way.
In the same way, DPS jobs consign all of their group utility to cooldowns that do not affect their performance.
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. The only break in this is that Sage has a single charged action to very slightly break the monotony, but to nowhere near a sufficient degree to make the experience palatable.
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 utilise 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, meaning that losing interest in the role as you become experienced in it is quite horrifically entirely intended and by design.
Healers are unnecessary.
Encounter design in this game is very rigid with almost no unpredictable damage spikes. Healing through or mitigating unavoidable damage could be handled by giving all jobs a PVP-style recuperate action and limited access to self-raises.
Original post below:
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.