I don’t quite follow your arguments. X11 got big and bloated, wayland applications need to worry about the different compositors? So we should use one implementation? Implementations should be irrelevant. That is the whole point of an API/protocal - a description of how things should talk to each other even for different implementations.
I don’t see how one implementation helps here - that one implementation still needs APIs for the applications to talk to. The problem is not that there are different implementations but maybe that the wayland protocol does not cover enough of the API space needed by applications. Some of which are addressed by things like the xdg-desktop-portal.