Love the last line, what Valve has done on Windows emulation is herculean, I don't know (it would be great to know) other businesses creating/investing in incredible and risky third-party compatible technologies to run their real business on top of it.
I worked in what other calls "Adversarial Interoperability" [1] but the scale of Valve is on another level.
[1] https://www.nektra.com/main/2020/01/12/reflecting-on-16-year...
On the hand at one point the emulation layer becomes the target. Hopefully game developers will realise this and start using native Linux technologies before they are tied to a single companies abstraction layer. Again.
The XBox was named after a Microsoft API. Definitely one of the more clever ways to force developers to eat your dogfood.
When it was created DirectX was a really useful thing for game makers. It made it easier to write hardware accelerated applications that were also consumer friendly. Contemporary Windows is full of anti-patterns. MSFT just can't seem to resist sticking things into it that make it less pleasant to use in support of MSFT's ecosystem. It's no wonder Valve invests into trying to be independent of that.
Wine is more stable as an API to target than any of the native Linux technologies.