The comparison with OS/2 only applies at a very surface level - and isn't even the whole reason why OS/2 failed when it had to compete with Windows. Among other things:
1. OS/2 could only run 16bit Windows applications at a time when Windows was switching to 32bit. Even the 16bit Windows applications were not 100% compatible and that is despite using Microsoft's code.
2. OS/2 had much worse hardware support than Windows as everyone was targeting Windows. On the other hand IBM as a whole never put much effort towards OS/2.
3. OS/2 Windows support had applications either run inside an isolated environment or they looked "alien" next to OS/2 applications at a time when GUIs were still trying to look consistent. While this is also the case with Wine/Proton, the focus on games makes this point moot (and people do not seem to care as much about GUI consistency these days).
> Now with Windows based handhelds, Valve will learn what happened to netbooks.
So far every single Windows handheld review i've seen that compares it to Steam Deck mentions both how the UX is worse than Steam Deck and games are -ironically- more likely to have issues on the Windows-based one. The only two saving graces for Windows handhelds is that they tend to be faster (but only when running at full throttle which limits their battery lifetime - Steam Deck runs faster at lower watts for better battery lifetime) and that anticheat rootkits work on the Windows handhelds whereas they do not work on Steam.
And you also forget that Valve did try to get game developers target Linux and put a lot of effort in the ecosystem for literally years before making Proton, yet developers largely ignored that.
Microsoft is already half way there with WSL, as soon as they realised folks rather buy Apple gear for UNIX experience, instead of supporting Linux OEMs.
"Runs Windows better than Windows" didn't work last time, and won't now.
And if XBox really goes full speed ahead as cross platform brand, as the console rumor mill has been discussing, lets see how many Microsoft owned studios stuff keep landing on Steam.
It already works, i play games every day, pretty much all games i play are Windows games and i can count on my hands the number of times i booted on actual Windows the last three years.
It suffices for Game Pass and Epic Store to be more appealing to studios targeting Windows, plus all Microsoft owned studios being taken out of Steam.