I wouldn't call having only a subset of system calls, no containerization, no background services, no proper init system, no kernel modules, "not all that limited". But maybe that's just my use case.
I've never hit a system call I wanted but wasn't available on WSL. In fact the couple times I've been disappointed at the lack of a system call it was when I was booting linux.
No containerization: Agreed, this is a significant limit.
Background services work just fine, I don't know what you're getting at. I have cron and stuff going.
What's improper about the init system? I start services, I stop services, it seems fine.
No kernel modules: I feel like this is pretty niche.