That said, I think most of us, except for the die hard purists, are fine with Proton compatibility being the main target for companies. As long as a game runs as well as it does elsewhere without restrictions or inconvenience, most of us are happy and don't care about the technical details of how it's running.
If we talk ABI's not API's, it's not a joke https://blog.hiler.eu/win32-the-only-stable-abi/
It's funny because it's true. Valve took advantage of Microsoft API stability guarantees and executed with an overnight success 10 years in the making.
It's actually a great thing, too. You build a game once and it's more stable than any distro packaging could ever make it be.
So less avoiding Windows licences and more avoinding getting cut out by MS.