The only times it's OK are when it's planned for specific softwares. For example, I can't run Rocksmith 2014 on native Deck but it works fine in Windows. Similarly, software that's OS limited would be another use.

But if your main thing is gaming, and you aren't dual booting... Yeah, I'm judging you. (And I mainly use Windows on PC. But why, why, why would you need to only run Windows on a Steam Deck without a specific purpose