(Replying to myself because it is too late to edit.)

I found a shorter reply to your comment, which I will now write:

>when it comes to the GNU project and the whole Free Software movement is the ability to run _any_ program, be it non-free software or free software.

Just because the GNU project allowed non-free software to run on GNU doesn't mean there existed in the 1980s a userland that would run on GNU if GNU had consisted of just a kernel (or just a kernel and a C library and a C compiler).