> it is entirely an OS in an academic sense - in scientific literature OS == kernel, nothing else

No, the academic literature makes the difference between the kernel and the OS as a whole. The OS is meant to provide hardware abstractions to both developers and the user. The Linux world shrugged and said 'okay, this is just the kernel for us, everyone else be damned'. In this view Linux is the complete outlier, because every other commercial OS comes with a full suite of user-mode libraries and applications.

There really isn't that much GNU on a modern Linux system, proportionately.