Thank you for explaining what Wayland really is: a protocol. I see way too many people in forums going "Wayland constantly crashes" or "this doesn't work with Wayland" but what they actually mean is that their compositor of choice crashes or lacks a feature. There are a few things that Wayland doesn't support (like multiple-main-window-apps that want to put their children relative to each other (i.e. multi-window Gimp)), but that's usually not what's being discussed.
But please allow me to correct you on a few details:
X is not a server. X.org is the single remaining "big" X server in use which replaced XFree86 a long long time ago. X is commonly available as a shortcut to start the main X server installation though.
X11 is not "an unmaintainable mess". X11 isn't as simple anymore as it used to be, but certainly not in an unmaintainable manner. But writing a new X server from scratch is about as much work as untangling the unmaintainable mess that is X.org
far more efficient than with X11
In theory. The issue is that, at this point in time, the vast majority of software that actually needs this efficiency (read: video games) run on XWayland, which adds a bit of overhead which ultimately causes them to run slightly slower on Wayland compositors compared to X.org. Maybe this will change at some point as devs patch their native games to check for a Wayland compositor by default and the big set of Wayland-support-patches makes its way into wine (and hopefully proton).