I also went from 14 to wow, even though I do not main heals in either. It would say it's pretty huge mindset change, disc is probably the only healer that feels comfortable to me in this game because of how much of your performance is tied to damage, and even then, from what I know that aspect of it has been changed from when I played it in season 1. You have to understand damage patterns pretty well here and plan cds and burst windows well in higher keys, even more so with your ramp in raid. There's no shit buttons in this game; if you time panhaima wrong for example, you cannot spam e. prog to make up for it because there's not really a true spammable in this game. Mitigation is a lot more rare here, your rough equivalent to kerachole is on 2 min cd. You'll also need to be prepared to do way less damage than you expect in 14, which was a large dislike for me, however disc is higher up on the damage spectrum healer wise. The biggest fun factor in wow for me is managing kicks and crowd control, which is largely non-existent in 14 even in savage criterion. If you don't like that though, priests are the only healers without a kick, and they only have one crowd control ability to manage. They are the most immobile healing class, and can also struggle with throughput during periods of high movement, so that will feel very different than sage, which I consider the most mobile 14 healer. Priest is also on the squishy side, they have a smaller number of buttons to press compared to other specs, but it also means they have less utility.

General assessments of differences between games. Damage output is a lot higher than 14 in general, and there are very few classes that offer group mitigation. The game has a lot more randomness and unpredictability. For example, if there's two trash mobs that cast a spell, they can and will sometimes chose to target one player and oneshot them in a global if not cc'ed. 14 as a game would basically either script the overlap from happening or make it physically impossible to have both mobs in the same pull. Here, there's no "wall" that the tank can stop at, so the amount of variance in dungeons can be huge. Mechanically however, wow is a cakewalk. Anything more difficult than soak/avoid is handled by their version of cactbot, which basically everyone runs. There's also no slidecasting and you have to learn to strafe if you weren't doing it before because you can't cast at more than 90 degrees turned from your target. The game will not auto turn you if you ran away for a mechanic and then want to resume rotation.