There is big difference in responsibility w.r.t. users in Xserver vs wl_roots case.
In the X11 case, relations are:
wm - user - X11
(Users choose to use Xserver and WM independently, if there is a bug in Xserver, then it is outside of responsibility of WM developers.)
In the Wayland case, the relations are:
user - wm/compositor - wl_roots
(Users choose wm, wm developers choose to use wl_roots to implement wm features instead of doing it themselves, but that is just internal implementation issue of that wm and wm developers are responsible for wm behavior/bugs including ones inherited from wl_roots.)