I aggree with the sentiment that WoW probably came out in the right time and did the right things right. It was the casual players MMO and one part of its appeal was, that it had plenty of solo player quests that allowed players to reach max level without grinding mobs for prolonged periods of time or being forced to play in a group, they could just level on their own and get groups when it was to their convenience. Though actually most healers being that restricted was mostly a problem for the first raid tier, even during Vanilla WoW, Blizz managed to give the healers each a strong distinct identity in what they are doing. Druid was the HoT healer, Paladin was already going in the direction of chunky single target heals and becoming the most effiicent tank healer by the time Naxxramas hit, Shaman was the group aoe healer and Priest was the all in all Jack of all Trades. Thats all in all more than we can say about the FF14 healing classes and healers roughly kept their identities while at the same time transitioning to a more modern action-focussed playstyle that added to that identities. I think in that regard, WoW also did the transition to healers dpsing quite well, which I think is an inevitability for a modern MMO in which mp-management isn't enforcing total downtimes. Especially since in WoW, healer dps actually improves on the class fantasies. Paladins and Monks should be on the frontline, battling foes while healing their enemies, the discipline priest feels like some sort of Inquisitor balances light and darkness and Druids cat- or owl-weaving is making this old fantasy of the versatile druid who can fill in different combat roles. Being a former Paladin Main myself, modern Paladin design is my absolute favorite, because why shouldn't a holy Knight in full plate armor with a hammer and a shield not being out there in the melee?
To be honest, I don't think that the problems of FF14s healers go that deep in. There are some superficial problems with the games design, but I think the biggest difference is, that it just doesn't feels like the devs have anybody in a position of authority who actually plays or understands healers. Healer Design feels catered towards people who don't even main healer, but who pick the role up to get faster invites at the occassion and don't want to be bothered and pushed to heal too hard. It doesn't help that the devs obviously adapted dps checks to the reality of healer dps, but never bothered to look into the issues and reality of that playstyle. Healing overall feels like designed for people, who consider the role a chore tbh, when in reality, it should be easy to pick up and just engage with casually on the starting level and from then on allow for more and more complexity up to its highest levels, which I feel like is left out.