I daresay the Ubuntu userspace WSL ships with absolutely eclipses the kernel in terms of lines of code. For all intents and purposes it's another Linux distro, essentially with just one or two core packages swapped out.
Excluding drivers, documentation and non-x86 arch code, Linux is "only" 173mb of uncompressed source (39mb gzipped). The Debian source repository is 103GB compressed, or, put another way, the replaced code amounts to about 0.03% of what makes up Debian.
Turning that on its head, if you removed all of userspace and just left the kernel, would it be truthful to call what remains Linux? I'd say in common parlance that is what's called "the Linux kernel", and what people mean when they say Linux more thoroughly refers to the work of distributions than it has anything to do with the kernel
Linux of the early 00s was popularized on a platform of "Linux is about freedom, Linux is about choice". At least one half of that is entirely due to the distributions.
From a programmer's perspective, you are writing a program which interacts with the world by making system calls to the kernel. So the kernel is fundamentally more relevant than the fact that the system is running Wayland and comes with LibreOffice.
The Linux Subsystem for Windows is good enough for my software development needs - the Docker Engine does not run in WSL but you can tell the Linux docker client to use the Windows server by setting an environment variable:
The point is that unless you are fiddling with the kernel, a Windows laptop with WSL makes for a great workstation for software developers. Even if I only develop for Linux, for me it is either a Mac or Windows on the desktop (my pet peeve with Linux on the desktop is the several counterintuitive paste buffers).
As a reimplementation of the kernel APIs on top of the NT kernel, it's not the Linux kernel, but it is more than just some GNU tools. In theory, eventually nearly any Linux application should be able to run on WSL.
Excluding drivers, documentation and non-x86 arch code, Linux is "only" 173mb of uncompressed source (39mb gzipped). The Debian source repository is 103GB compressed, or, put another way, the replaced code amounts to about 0.03% of what makes up Debian.