How can I disable XQuartz entirely and use Xorg with my own Desktop Environment?
If I have understood you correctly, what you actually want to do is to get rid of the Mac graphic environment, and run a "classic" X11 session instead. Correct?

I don't think you can get rid of the Mac graphic environment entirely (short of installing some other OS, like *BSD or Linux), but you can hide it to a certain extent.

Configure Xquartz to run in full-screen mode (it's in the settings somewhere...). This means you won't see any Mac stuff. Create an ~/.xinitrc file. Xquartz will run that file on start-up, just as would normally happen with startx or xinit. In that file, you can start any window manager you like. e.g. good old twm. (If you don't have an .xinitrc file, Quartz will start the quartz-wm window manager, which gives a "Mac look" to your X windows.) It should be theoretically possible to get an entire Gnome desktop running, but I have not tried that... You'll still have to boot into MacOS and log in to a Mac desktop, but after you have started Xquartz, you should be back in familiar X11 land.

(I get the impression that you believe Xquartz is the standard graphic Mac environment. It isn't. Xquartz is an X server that runs on top of the Mac graphic environment. I think Xquartz is just a packaging of the Xorg server, built for macOS, but I could be wrong on that.)