That's what it boils down to, isn't it?
SE is scared of letting healers fail. It's fine for tanks and dps to be able to fail but for some reason, healers must be exempt from this.
And I don't even think they're trying to do healers I favour there, I think they're more focussed on minimizing or outright deleting anything that could interrupt the flow for the rest of the party in case you get a worst case-healer.
The moment a healer could do something that results in unpleasant consequences (not that a death or even a wipe in any content is that bad) they're ready to screw the training wheels on again.

I liked Carby in that regard because despite the fairly frequent raidwides (21 vs 15 within ~9min compared to p6s), the raw damage is not that far above the average HP pool so it doesn't take much to just survive and deal with the healing afterwards.
And I feel like while teaching people to use mitigation is important, hits that don't one-shot as easily but are more frequent send a better message.

But I personally believe that if a healer is doing highend content, there should always be a certain understanding of their toolkit.
I do not care one bit about how much a dungeon might have coddled them, if someone is in a reclear party for savage fights, they have to know what their skills do. Period. No excuses there.
Testing the waters in practice parties, experimenting with timings and miscalculating and so on is fine. You have to get a feeling for the damage patterns and that is best done in practice, not in theory.
But I draw the line at not knowing your toolkit and what skills even do and that is something I see more often than I don't. Almost every time I try to coordinate a little bit, as a matter of fact.
Over the past 2 weeks I had exactly one healer that didn't reply with some form of "no idea what you mean xD / uh which skill? / one sec, need to bind it / no idea xD / uhm I'll just see, sometimes I use it there, sometimes not... I think?" when asking if use a big cooldown at specific times or could use them at specific times (e.g. Lilybell on 2nd tumult, Seraph for stack/ spread etc).
No elaborate mapping for all the buttons, just 1-2 skills on a long cooldown.