It's radical, I know... but here it is.
You want a healing job that heals and only heals? Low stress? Low demands? Can wear any healing gear that drops and can participate in most content? Look no further:
Conjurer.
It's simple. Take out the WHM job stone, remove any complex DPS systems that the WHM could have for new players. Give Conjurer only skills when WHM gets skills and replace those skills with the WHM skills when the stone is slotted in again.
Conjurer can already wear all healer gear. It may even be able to use WHM artifact weapons (I'm not logged in to check at the moment). Hell, give the lily system to the conjurer and make a different system for WHMs.
No needing to punish AST/SCH/WHM players for wanting DPS tools or utility/buff spells. No need to suffocate WHM with this idea of needing to have more heals. Make the advanced healing jobs cater to playstyles of the people who want more complex mechanics. Leave conjurer and support it with CONJ-only spells at higher levels for those who are afraid of these things and simply just want to heal. No longer do you need to worry about stressing healers out because now healers who are stressed out by dpsing and buffs have their one go-to job for all things healing.
Conjurer doesn't really have to be subject to the same balance as the other 3 jobs either. More demanding content like savage and that should require more demanding jobs. Hell, I am not stressed by healing, hate the 5.0 changes to just about all the healing jobs and I don't even DO savage content because I just don't like that sort of content and would never do it with people who aren't friends.
So there you go. Instead of neutering all jobs, support the base-class Conjurer to higher levels and use that as your "newbie friendly, low stress, healbot" healer.