Anecdotally, I strongly doubt this is true, although my environment is probably quite biased. I know a ton of people who use Gnome, some who use KDE, and I think roughly all of these people use them with Wayland. The standalone-WM users I know are also mostly on Sway or other Wayland ones. The only real X11 holdouts seem to be people using X11-only DE's, such as Xfce or Cinnamon.
> I think roughly all of these people use them with Wayland.
While we're making unfounded statements based on our own anecdotal experiences: can't speak for Gnome users (very few in my circle), but for KDE and tiling window manager users, it's a lot of X11. Hard to say exactly, but would put it at ≥50% X11.
Xfce is working on Wayland session support. It is working now with some limitations (limitations on what you can embed in the panel are all that's left, I think).
Pretty much possible to use gnome and x11 (until now).
Personally I have given up with wayland as in years ago. There will always be something I should not have wanted to do in the first place while using wayland. I would rather use x11 and have much better control.