This has already proven to be wrong, imho. There's numerous Wayland versions of popular niche X11 WMs, for example the way sway is a Wayland implementation of i3, and some exciting new experiments (like scrolling tiling WMs) that never really existed on X11.

It's usually a lot easier to make a compositor/WM with unusual or innovative behavior on the Wayland stack than it was with X11 in general, as far less behavior is presumed/baked-into either the display server or the existing applications. For example, apps not being able to introspect or manipulate their global coordinates also means the compositor can arrange them however it wants without breaking app assumptions, which enables fancy new layouts.

There's prominent libraries that make compositor development easier, for example wlroots and QtWayland -- XFCE is also using wlroots. "Punt it to a library" isn't radically different from "punt it to Xorg", even if the slicing is a little different.

The tail looks alive and well.