Yeah, so is not shitty for those claimed X11 devs to drop X11 since is hard and make a spreadsheet with a specification of a subset of X11 , then let other suckers implement it and maybe some other suckers create specifications of the missifng part they refused or were incapable to create. Probably all was exactly as Red Hat planned, if it works for GNOME then the rest is ignored or if it does not work for the rest then is a bonus.
> The wayland protocol is essentially only about input handling and buffer management
So sending input to clients and managing the buffers needed is what wayland implements. Everything else is either done in the clients (e.g. rendering) or the compositor (pretty much everything else).
Note that this is a subset of what X11 did (though rendering had pretty much already moved to the client for modern applications). X11, of course, handled input, and it also provided an IPC mechanism (which is how clients e.g. communicated things to the WM). Wayland, at its core, is just those two things.