Not really too much to add outside of saying this is a very important topic. So many of the "healing is too easy" and "healers are boring" perspective is from A.) those who have a ton of healing experience and/or B.) those who heal with/for a community (maybe even a static) of higher skilled players. Not all, mind you, but I would wager a significant portion. That certainly doesn't invalidate their perspective but it does highlight exactly what the developers themselves have pointed out. The healer archetype they tend to create is not really aimed at the more experienced, higher end player for better and worse.
I'm not a healer main by any means, but my personal experience tends to fall in line with the OP. Often when I do decide to heal, healing is pretty much occupying most of my brain space. I appreciate the simplified DPS. At the same time, though, I use AST when I do heal not only because I love the aesthetic but also because I appreciate that it is a little busier and more active outside of the healing requirements due to the card system and the time delay mechanics. Playing WHM bored me to tears because I really did find it too simple, so I do understand why more experienced players would want more. But, when I am healing, I just don't have the expertise to think about much more than healing if things start going south (which happens often considering when I do heal it's usually with more casual groups).
So, yeah, I'll just say that I don't envy the devs in having to appeal to me, having to appeal to those with even less care/ability/experience than me, those at the absolutely top of the healer food chain, and everyone in between. Healing really is the one job where the demands on the player can really be the highest and the failure point the most detrimental but the player level in both skill and interest is all over the map.