Historically operative systems was named after their kernel because each individual user put together the program that they wanted in their system. The actually term used was "Linux based operative systems", which comes from users starting with a linux kernel and then built everything else on top of it.

GNU is a project to create the individual parts which users need to make a operative system, which is why Stallman calls it GNU based operative systems. This is also attached to the historical context of users building their own systems by assembling parts to compile and run.

While we should recognize their historical and current contributions, Debian is based more on their community and policies than on any specific package.

Agreeing with all that, the distinction isn't made in general speech or writing.

MVS, CMS, VMS, OpenVMS, UNIX, Ultrix, Solaris, AIX, HPUX, DOS, CPM, BSD, MacOS, Windows, BeOS, iOS, Android.

GNU/Linux.

There are times you might specify the user environment. MVS TSO/ISPF, say. Or hardware: VAX/VMS, SolarisX86. But not elsewhere the libraries.

I get RMS's rationale. I largely support and practice it. But it runs against convention and practice through the rest of the industry, for decades.

And mentioning Debian, it's also available without Linux.

Though I agree also really packages & policy.