I don't know why exactly, but Square seems to be hellbent on making healing the official "I want my non-gaming friend to play with me" role. DPSers get complex rotations, tanks have been turned into DPSers with defensive cooldowns, and then healers get Fisher-Price "Baby's First MMO."
They want healers to be "pure healers" and not DPS, to the point of actively removing most DPS skills from healers (making them incredibly, mind-numbingly boring to play the MSQ with), but they're terrified of deviating from perfectly-scripted fights or doing anything that even remotely stresses the healer (like The Vault or Aurum Vale did), seemingly out of a fear that healers are babies who will get scared and run away at the first sign of a challenge. That's the only explanation I can come up with that makes any sense: healers are the dumbed-down role by design. It would explain why they don't see anything wrong with the role, why they're so dismissive of healer complaints in the Live Letters, why nobody on the dev team plays a healer, why DPS and Tank jobs get all the interesting design and shiny toys, why there hasn't been a new healer job for two expansions in a row, etc. It also explains why healer design is in such a bad place, when the rest of Shadowbringers is positively bursting with quality, from the story, to the music, the tank/DPS class design, and the new trials and raids; this makes incompetence unlikely as an explanation, which suggests that healers are stupidly easy to play because Square wants them to be stupidly easy to play.
And short of Yoshi-P forcing the job design team to sit down and Malefic-spam all the way through the MSQ, from ARR to ShB, as healers, I don't see how this is going to change.
