

I do think Proton gets a little too much credit.
Why? Valve has been sponsoring all these projects for a really long time. While wine existed before that, it wouldn’t be anywhere near the shape thats its currently in because gaming was not its main focus. There have been loads of gaming bugs and sharp edges that have been around wine for a long time until Valve put in the money and devs to fix them.
Because DirectX is more than a graphics API.
https://en.m.wikipedia.org/wiki/DirectX
A fair amount of what used to make DirectX an everything API has been deprecated, but if you are already using Windows stuff for networking and audio, then you may as well use the graphics APIs too.