When picking up a healer class, it's already very easy. But that's alright, first not to scare away people from playing them, and secondly to not overwhelm new players. The DPS classes also start very easy.
The main difference is that while most DPS jobs get some kind of depth or complexity by getting their rotation expanded (some are quite easy to play even with less practice, but others at least need you to pay attention to do halfway decent DPS), healers don't.
Healers, instead of becoming more complex, become easier to play with higher level and better gear.
Now, not considering the DPS part of healing, but just the healing aspect, when you get stronger healing tools, especially the oGCD heals, healing obviously gets easier, because you obviously have more tools to heal damage faster. Even though the encounters (talking about casual content here, because in savage you would try more than the minimum anyway) don't become that much harder. But this is natural.
Adding DPS, it doesn't even get harder directly. You can misjudge when it's safe to DPS, but when you're not sure if it is (because you're new for example), you can just choose not to, and cast a safety heal instead. Meaning, as long as you put in some effort, it's perfectly alright not to maximize your DPS as a new player, or in new content, or with a struggling party for example. Like some people give the advice 'at least try to keep up your DoT'.
What I don't understand about this all is how there are players that still find healing very challenging, when you can get away with only ever casting your GCD heals - and take that as a reason to be against healing being more involving.
I mean, you can't make healing casual content so hard that new (or bad) players are totally unable to clear the content. And if all your party members don't know the mechanics you will have a difficult time keeping them alive even if you're a veteran. So the actual direct healing part of it must stay manageable. Only the 'becoming more efficient' part of it can become more complex. Things that get you more time to DPS. Which in turn could also become a little more complex without making playing healers become that much more difficult.
But there are STILL topics about how healer DPS is already challenging enough as it is, and how people couldn't keep up if it were even slightly more complex (even if it was in the past and people managed with less oGCD heals as well). How having any kind of proactive instead of reactive healing would be too much for them to handle (that's why some ASTs don't use Earthly Star I guess). There are people who, even though they would welcome a little more complexity, defend this attitude by saying that at least one healer should stay very simple for the casual players.
Of course people suggest that this healer should be WHM. Even though WHM would be the best example for more complex DPS, BECAUSE it has the least buttons and no extra mechanic to concentrate on. But no, it absolutely NEEDS to be easy and accessible, and even more so at max level - it's not allowed to need some thinking to get more than the basics out of it.
A DPS player that doesn't care about their rotation just presses whatever buttons they want to. But when there are suggestions about making healer DPS a little more engaging, people cry about how they want healers to be really easy to play. Healers would become a bit harder to master, but for players who have no interest in that not much would change, wouldn't it? It would only change for those who find pressing Glare/Broil/Malefic too boring.
What do you think about the difficulty of the healers?