What is this “massive fragmentation” you speak of?
Anecdotally, I’m using Plasma, and every Gnome or Gtk app I’ve tried appears to be working perfectly, and vice versa when I occasionally try out Gnome.
Much less so for DIY/BYOB desktops like Hyprland, but I feel like that’s what you sign up for there.
That's one of the things that freak me out about Wayland.
The DIY/BYOB experience is perfectly viable in the X11 world. I don't think I've ever had a piece of software balk at me because I used FVWM instead of kwin. I don't want to be railroaded into a desktop environment with strong opinions and mediocre tools when there's a sprawling flea maret worth of software to explore.
https://wayland.app/protocols/
Click any protocol, very few outside the core and absolute essential extensions have universal support.