This only holds true if your idea of a "complete distribution" is the desktop environment. Gnome team doesn't do work on kernel, core tools, package managers,

This only holds true if your idea of a "complete distribution" is the desktop environment. Gnome team doesn't do work on kernel, core tools, package managers, init system, drivers, etc. While gnome contributes important work to the average desktop user, most servers run distros with no gnome packages, and even no desktop. Linux is a lot more than a window manager and associated applications.