After years of mesmering, I've come to the conclusion that my heals are bad.
Technically, I already knew this since I've used various means of supporting it (food, for instance) but it wasn't until recently I realized that there was something seriously lacking to begin with in the core profession.
Why are they bad? Very simply put, between managing clones and wells and aoes, I rarely have the time to heal up as well. So the reason I fail is almost always not being able to pull off a heal when it's needed, which is constantly unless we're talking low-level mobs and they're never a concern anyway.
The thief profession handles this much, much better; you can add plenty of sustain with heals on using initiative, heals on crits, heals on attack, heals on evade, heals on struck with low health.... you can find the level you want easily and actually focus on playing. Elementalists have a much better balance too, I find, and these are the professions I would compare with with a similar high mobility squishiness playstyle.
All I've got is the crappy Ether Feast and random chance. Avoid being hit? Good in theory, in practice this is the reason why playing mesmer well is difficult, especially since it's all about the shatter these days. We can't all be mirages, you know. Being hard to master is one of the things that drew me to the profession, but y'know what? Artificial difficulty isn't what it should be like. Yes, you can be pretty godlike provided that you have the time to git gud and maybe I'll get there too but that's irrelevant because it applies to everything.
The point is that few of us have that much time to put in and that's what leaves mesmer a crappy class for everyone beginner to moderate. Very simply put, the class should require less micromanaging and thus less elitist so that we may be enjoyed by everyone. Balancing is the name of the game.