> we would have been better off had Wayland just been a X11 extension.

That would have never happened. From a functionality standpoint, Wayland is "the parts of X11 modern toolkits actually use". Give clients a buffer, have them locally render into that buffer, then composite the buffers together into a final display. Xorg can do all this. It's just a question of, do we want the maintenance burden of all the other stuff that Xorg has, like obsolete graphics primitives, obsolete visuals, etc.? And do we want the architectural decisions of X11, which seemed sensible in the 80s, but make far less sense in light of modern GPUs and modern applications with modern display needs?

The point of Wayland always was to start from scratch.