>that Wine/Proton helps make the Win32 and DirectX APIs a sort of de-facto cross-platform standard when it comes to things like desktop gaming, and that this is a good thing for them.

I'm not sure if it benefits microsoft in the long term, because the "backwards compatibility" features of Wine need to be implemented in Windows already as a part of the system. So in the long run wine/proton/mono will implement windows features on linux in an optional/replaceable/modular way in user-space while keeping backwards compatibility for older windows software, while windows is forced to implement (and distribute these features) with their OS and has to sacrifice backwards compatibility if they want to simply their OS.

I would say that the adoption of wine/proton helps the linux ecosystem a lot more because there wasn't a standard executable format for linux beforehand (static? tarball of program and dynamic libraries? .deb file? AppImage? Flatpak? Higher-level language like java?). How do you reliably link to libraries like mesa or even glibc? Now there is a solution: just distribute a windows program and test it to confirm it works in wine/proton. Perhaps it is better for DirectX adoption, but it seems like Vulkan/OpenGL/WebGPU are still superior in terms of cross-compatibility, regardless if you use wine or not.