It's really bizarre, the way healers and content continue to be designed in opposition to one another.
They want healers to have the responsibility of repairing mistakes. We know this because of several reasons: regardless of the offensive tools available to healers, they output the lowest damage (including offensive support), so their value naturally has to come from what they do beyond damage, which is to say, healing and utility. Combat has been designed with the philosophy that unavoidable damage is rare and avoidable damage is frequent. The amount of healing required for unavoidable damage is low enough to where non-healers are capable of handling it in many forms of content, thus the extra healing and utility provided by healers seems intended to respond to avoidable damage. Yet difficult content largely makes avoidable mechanics result in wipes, so even when a party doesn't do something correctly, that excess healing can't resolve the problem.
It's not even like healers are actually designed to be that child-proof. In many ways, they have child-proofed various healer elements, but there are still several things that seem designed to hold back the novice healer while providing nothing of value to the experienced healer. Take MP for example. MP restoration is effectively automatic--it's sustained through the on-cooldown Lucid Dreaming and resource management systems of every healer with most actions that cost MP only costing incremental MP taxes that are otherwise resolved by the automatic MP you get from just playing your job correctly. An experienced healer isn't particularly concerned with running out of MP outside of raise-heavy circumstances, but the novice healer is the one who might sit on their resources or forget to use Lucid Dreaming. The vast majority of healing tools we get are OGCD healing tools which require weaving to maximize their value. Who's the one who's most likely going to idle or clip their GCD? The novice healer. If they really wanted to child-proof the healers, they'd do things like give Medica II a 15 second cooldown so you literally can't recast it until the regen has finished.