If I understand it right, it's a GNU/Linux distro without a Linux kernel on top of a compatibility layer on Windows, right?
So "GNU/Windows NT Kernel" is better than "Linux" - That actually one of the rare few occastion a typical "GNU/Linux" distro gets used without the Linux kernel part.
But because "Linux" has brand recognition, it's still used.
(*): there's no separate compatibility layer (unlike things like Cygwin which are a user-mode compatibility layer that translates POSIX API-calls into Win32 calls - and thus enables soure compatibility).
The NT-Kernel has a bizare peculiarity : it can export several different ABI's to usermode software - it has different "personnalities".
- Win32 is just *one* of the set of ABI available.
- A long time ago, that made it possible to run OS/2 software on Windows NT.
- A little bit less longer time ago, Windows NT also had a "Unix" personality.
- Now WSL is actually the NT kernel exhibiting a small subset of the ABI featured by the linux kernel - about the bare minimum to get a few basic user-mode software (e,.g.: the "GNU" part of "GNU/Linux") run unmodified.
These are straight ABI available from the NT-Kernel, not a mere Linux-to-Win32 API conversion like Cygwin.
- Among other defaults Win32 has a poor multi-processing (forking is expensive). Cygwin application have to rely on that poorer cousin in order to provide multi-processing to POSIX.
- The recent kernels of Windows NT intoduced pico-thread which are very cheap, weren't available in the Win32 API back when introduced, but where exposed through the "Linux-lite" API that is WSL in order to make a usefull multiprocessing.
On the other hand WSL is far from complete. There is tons of stuff that you can do on your GNU/Linux that you can't do with WSL (e.g.: filesystem drivers)