Counterpoint: I don’t think any Linux DE will ever see mainstream adoption.
It has nothing to do with how good they are. It’s not related to software support either. They could support every piece of software ever made; Linux supports 90% of games for Windows and emulators for dozens of other platforms and it still hasn’t attracted more than like 2% of gamers.
It’s related to what OP said: to gain mass adoption you need to put up with a lot of bullshit. It takes a company with some financial gain to do that, and paid developers. Volunteer contributors will eventually say “screw this” or go mental like Torvalds.
There’s no company that can do this. They tried and failed, because Microsoft. Apple and Google had to create their own platforms from scratch to get away from it.