Yep. The only compositors of any significance that do not use wlroots are Gnome/Mutter and KWin. I guess Weston is also an independent compositor, but I don't think anyone actually uses that.
Weston is mostly used for car entertainment systems, as a replacement for Windows CE.
It, along with the more modern wlroots-based alternative Cage, have become the de-facto Wayland window manager for when you don't actually want to display framed windows, and just want to fork the codebase and display some fullscreen GLES-based graphics in a kiosk instead. These IoT use cases were part of the original motivation for Wayland in the first place.
I'm on proprietary NVIDIA, so haven't actually quite joined the Glorious Wayland Master Race yet. I use Weston on X11 to host Waydroid for my Android game development. Works rather well. I hope Weston development doesn't end up moribund because a few folks like me actually use it.
It's not dead, but it's gotten way more patches upstreamed from the automobile industry than anything desktop related. So any sort of Linux desktop testing is likely very minimal.
