File system performance sucks. No fuse support. No direct hardware access. I've experienced stability issues with it. Don't get me started on the networking or custom init put in by Microsoft. Systemctl calls don't work.

It is most definitely not just like regular Linux.

I actually used it pretty extensively for years before I figured out it was causing more friction than it was worth. It's convenient, I'll give you that, but again, it's objectively worse than the other tools available. You should try them.

What's the big deal if he likes it? It works for him. It's fine.

Just because someone likes and uses something doesn't mean there aren't better alternatives that they could benefit from using and learning about.