No, there is Gnome’s, KDE’s, Weston’s (the reference), and Sway (wlroots)’s implementation.

This latter is pretty much a library to build your own de with minimal code up on top.

If that's the case, that there's no common code they're all built on, then why does anyone talk about "Wayland" anything?

All these conversations end up kinda pointless because of a sort of "it works on my machine[desktop environment]".

Well the conclusion is that it's never a wayland bug because wayland never defines X feature that users are missing.

That is a correct conclusion, in the same way that many issues with X features are not actually issues with the X server. Over the years a lot of things have been moved out of the X server into client libraries, or into Mesa, or into D-Bus, or into Wayland...