I'll grant that the standard shipped themes for most window managers are kind of lifeless, but that's just a function of popularity. Any such project that wants to have mainstream adoption has to...be mainstream, ya know?
Like, gnome/kde/etc can't ship some solarpunk slippy slidy tiling config for the same reason that Word can't save-and-exit with :wq
But the customization is alive and strong!
Compiz-style effects live on in gnome, cinnamon, hyprland...
hyprland in general lets you config just about anything.
WaylandCraft is a thing [0]
I personally use sway as I can just run all my windows without the chrome as windows are meant to be.
[0] https://github.com/EVV1E/waylandcraft
oh, and reddit link below the fold, but look at this thing and tell me customization is dead: https://www.reddit.com/r/hyprland/comments/1tw5x6e/final_ric...
Damn, that last link is killer.
So far I'm avoiding wayland (tried omarchy once, didn't really warm up to it), but maybe I'll try again.