More over, every "WM" in Wayland's case needs to implement the entire stack, even if it uses a common library for some of it.
And after similar length of development time, I'd say the result is still worse in many aspects than X11, and I say that as someone both using and praising a wayland-based compositor and lamenting that it pretty much locks me more than Windows used to
Well, if compositor supports server side decorations (and normal compositors should), I don't see how applications can behave weirdly becasue of that unless they are just buggy. It's up to applications to figure out if server side decorations work and use them if they do. I.e. even if it was a core feature, buggy applications could still behave incorrectly.
And I don't see Wayland being worse in many aspects, but on the contrary, see it being better in aspects which X11 didn't or can't address. I recently started using Wine Wayland for gaming and it's significantly better experience than using it with XWayland.
But if anything it's X11 that tries to lump a ton of stuff together. Wayland is very minimalistic in comparison. That's why stuff like libinput and Pipewire are part of making a functional desktop.