The point 2.1 "less to implement in the compositor" doesn't apply, because for xwayland go work (which is intended to stay around for the foreseeable future) mutter still needs to implement SSD, it's only skipping on implementing the Wayland SSD protocols.

Points 1 and 2.2 are not strong points. "We do because we always did before <thing 2>" is not a good point. For example, after all, we always used X10 before Wayland, and we always did implicit sync before last year. And compositor shouldn't limit programming styles, they should support as many things as possible, and let the application decide their programming design. Plus, most modern applications on windows and macos embed a copy of chrome to display a single offline Web page, but I don't see you suggesting we replace compositors with browsers.

Point 2.3 is also weak because most of the things a compositor does are already hard, but they implement them because it makes the experience better. If something is hard, it just means it will be worked on more. Take a look at explicit sync, it took like 4 years to be rolled out, but it was necessary and got implemented.

I'll give you point 2.3.1... in general I think KDE looks pretty bad, and gnome is really more polished in many aspects. Unfortunately I really prefer the KDE workflow on big screens (but gnome on laptops).