In my book WSL and VM share the same downside in that you're only abstracting Linux functionality in relation to the hardware.

Linux really shines when it has full access to the actual hardware as opposed to asking it's environment nicely if it's allowed to do something.

For example, I routinely need to change my IP address to talk to specific networks and network hosts, but having to step over the virtualisation or interpretation layer to do so is just another step, thus removing the advantage of running linux in the first place.

Sure, VMs and dual booting have their uses, but the same uses can be serviced by an actual linux install while also being infinitely more powerful.

I played around with WSL for a while, but you notice really quickly that it is not the real thing. I've used virtual box for some use cases, but that too feels limiting ad all of the hardware you want to fully control is only abstracted.

I would say that unless he has a really good reason why he wouldn't want to go for dual boot, then he should do just that.