> much of what is GNU emacs today was first in xemacs
Bit of an exaggeration there.
For one, xemacs' period of technological advancement, while it did last few years, ended long ago. The project's lists are nothing but spam nowadays and GNU Emacs is now much more advanced. In a project which dates back to 1976, the xemacs period isn't as large as one could think.
Another thing is that while the xemacs folk could borrow all progress from GNU Emacs, the GNU team got almost no code from the xemacs folk because the latter didn't document the copyright ownership of their code.
So the system was stacked against GNU Emacs, and it still won. They can't be doing too badly.