Well, want it or not GNU/ is a big part of Linux distros, at least until a distro with an alternative userland and c library makes it to the top. And even then most of open source has some GNU somewhere in the foundation.
There is also no requirement that a Linux distribution includes any GNU software at all, should we refer to them as e.g Busybox/Linux?
I don't agree with this actually, that's why I didn't even mention this. I believe GNU was indispensable to the wider Linux phenomenon. It's a matter of being fair and technically precise.
Alpine Linux (of Docker fame)
Lots of embedded stuff
Android shot past all the others to become the most popular operating system in the world, in case you didn't notice.
Not that it invalidates your point, but it has happened.
Alpine Linux (e.g. Docker) and Android