Would you, as a healer, truly be content with the tank doing once or twice their AOE combo every once in a blue moon to keep aggro? Yes, even in single target because that's enough and is still shinier than the single target one, usually, so bonus points for style?

Because that's what some of these arguments sound like to me. This is an extreme example, of course...inb4 anyone answers "Yes!": that would increase the dungeon/trial/instance duration by a significant amount. That's assuming DPS know what they are doing, which...isn't always the case considering they don't have just two buttons to DPS adequately. Yoshi-P said they aren't forcing healers to DPS in hard content, which makes sense because they have other responsabilities which fall to healers, such as healing checks and/or prey mechanics - but that doesn't mean they shouldn't. Devs calibrating numbers of a boss HP doesn't equate to them not considering healers at all, besides.

This is a game in which you are required to play in a team, so only doing what is strictly necessary is by itself a selfish way of playing - you honestly can't expect sympathy by doing so. Each class of each role has abilities which don't necessarily fit in the role they are in if you take it. While I don't pay anyone's sub, I'm pretty sure no one pays mine either -and yet I gladly do whatever is needed to make an instance run smoother or quicker, regardless of my role, including DPS as a healer. And I do expect just as much in return for my effort, because no one likes carrying lazy people on their back.