Why is the healer class basically a one spell dps class?

[Dzian]

CC got removed because people were sleep-gating mobs. That in turn evolved into the standard two pack gates we see now.

Partly true but the person you quoted was also right. People were complaining about cc being too difficult in a ton of early content..

coil for example, with having to silence high voltage in turn 1 to having to heavy / bind the golem thing in t7 and sleep /repose something somewhere (its been so long.)

Some of the primal to If I recall. Having to bind or heavy certain moogles to keep them away from the king.

Even LotA where you had to silence ancient quakes, heavy those slime thingies to stop them reaching the boss. And various other stuff that alot of the early content had.

Sleeping trash in dungeons was just a tiny part of the reason.