I'm at work in my iPhone, so responding to this is difficult. Firstly, in intense fights your triage target will oftentimes change multiple times a second (I'm assuming. I'm not end game yet but I have TONS of MMo healing experience. FFXI, EQ2, AO, Lineage 2, WoW, DAoC and countless F2Ps) Who needs the heal the most (balanced against how important the player is) will change. It happens. That's what makes healing fun. It's the split second decisions that make it engaging and challenging. With UI improvements, this is able to be pushed farther. Games with with sophisticated UIs allow for a higher level of decision making.
I started WoW a few months after release and at that time they had mouseover macros. They had addons that were just easier to use versions of macro and they had macros you could program yourself. I'm not sure what you meant by core feature but mouseover macros were in there from the beginning or soon after. So you're wrong there.
Also, ABC. Always be casting. I don't know how you play but as a healer, I'm always doing something. I will be interrupting, CCing, watching for adds, DPSing (if resources allow). I like to be the best that I can be. Sitting around watching bars may get the job done but I want content that is based around everyone being all they an be not content stiffed by UI constraints.
EDIT: Holy crap perfect analogy. The healing system in this game is like trying to make posts on a iPhone. It takes triple the time to do something half as well. If you don't think so try posting on an iPhone. Ugh, it sucks!