I do get it, but I don't agree with it.

You can't force your expectation about the game on any one, healer DPS isn't require to do proprer dungeon, it's only a bonus for really quick run. Most of the time, it doesn't ask more than two players to make a dungeon really smoother, no matter their role, and really huge fuck-ups to make it really longer. So if two player agree to kick someone, anyone, to get more DPS on the next roll they could as well just get things done themselves. Expert dungeon are the major pain to do, but they're the one with the overall better player.

Thing is, you missed the fact there's already a lot of healer that won't player with randoms because they don't want to deal with the shit in PF, and getting told they sucks. So they go in FC and so. There's a lot players who extremly low APM, or that aren't confident in content with other player and things like that. There's a lot of those player types on MMO with such large playerbase, and a lot of them ren't gonna grab the healers. Because they like that non aggressive take on the content, because they don't want high excecution based jobs. Some people may be leveling all job without being proficient about any of them. And that's all fine, these are way to play de game.

As a tool, dungeon finder is made for accessibility, not efficiency. When you use it, you agree to proc a dungeon quickly, but you don't choose with who end up with. that's the privilege of PF. I think player don't have the habbit of using it for quick run while it would be perfect for that. When you recruit your team like that, you can fix the rules and not just expect anyone to know how you want to play. I do see some farming dungeon partie sometimes, but I'm not sure why it's not more frequent. It's the right tool for what you want, PF is more about having less interaction between player.

But in the end, if you're the one finding the player you and up with not go enough, it's not everybody else that need to abide your rules. Most player will play the way they do because they think it's fine and to be honest, to game is more and the side healer doing only healing than healer doing DPS. The way Cure 1 and Cure 2 interact with one another is gonna make everyone think "I should use Cure 1 until free Cure 2 happen most of the time". And that's also why lilies were made the way they are, but it would a have asked a much more radical revamp on the game to work that way.