But that's the thing, nobody other that the GNU people called that an OS worth of a name. I suspect what people call an OS is an standalone set of conventions and packaging that can actually be used to interface between the hardware and the user [0]; so I think Debian is more worth of being called an OS on its own than "GNU userspace - kernel". Same with any other Linux distribution, *BSD variant, Windows and OSX. It was the linux project that made those OSes viable as standalone things (to be fair, the GNU userspace made them viable as usable working platforms for early adopters - but nowadays the role of GNU software in the OS is less central), and people place more weight to that.
But that's the thing, nobody other that the GNU people called that an OS worth of a name. I suspect what people call an OS is an standalone set of conventions and packaging that can actually be used to interface between the hardware and the user [0]; so I think Debian is more worth of being called an OS on its own than "GNU userspace - kernel". Same with any other Linux distribution, *BSD variant, Windows and OSX. It was the linux project that made those OSes viable as standalone things (to be fair, the GNU userspace made them viable as usable working platforms for early adopters - but nowadays the role of GNU software in the OS is less central), and people place more weight to that.
[0]: I pretty much agree with Ted Nelson about the distinction between "technology" and "packaging". (https://youtu.be/KdnGPQaICjk?t=1m47s)