I call that a bit crazy, but also crazy reasonable, because GNU really is the foundation of the OS, along with Linux.
The operative system running on my laptop and servers is called Debian. The kernel is just one of many packages available in the repository and can be replaced by a single command. Its not even the most significant important package, since libc has a higher impact during upgrades and package dependency.
And yes, I understand RMS's interest in GNU and keeping it in currency. And refer to "GNU/Linux" quite frequently myself.
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.
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.