That statement makes no sense. X11 works fine on macOS and running it in rootful mode with Gnome essentially works the same way it would work on an OS that uses the Linux kernel.

Granted, it will not integrate with anything hardware-wise by itself (unless there's a package for it - if not, macOS still handles it, and Aqua/Quartz will keep running in the background anyway), but if what you wanted was something that is KDE or GNOME running with its own WM on its own X11 server, doing the exact same thing you'd get if you're running a Linux distro, that's been natively possible for over 15 years.

If a power user loses their power based on what GUI happens to be in front of them, how much of a power user was the power user to begin with?

It's just a matter of what one is used to. As someone who's used macOS since before OS X was released (alongside Windows and Linux), moving and resizing windows rarely poses issues.