From what I've seen, almost all advice about making the switch to Linux is along the lines of "try it out" or "dual-boot Windows" so I fail to see how anyone is going to be seriously inconvenienced here.
As well, marketing in general is full of embellishments to the truth. Microsoft lies, Google lies, Apple lies. To turn around and say that Linux isn't ready for gaming when (using your charitable 10% figure) 0.2% of gamers won't be able to use it, is ridiculous.
You got lied too by Microsoft on the promise of hardware support and they pulled the plug. It feels like now you're trying to lay the blame at Linux' feet instead of copping that on the chin.
We're just circling back to the fact that WMR is a tiny subset though. You're holding Linux to an impossible standard that you aren't holding the maker of your headset (API) too.
You've talked about Linux as if it should meet these lofty goals, but what you're failing to recognise is that Microsoft pays teams of hundreds to thousands of developers, and Linux is completely free and donation/grant-based. So of course it isn't going to be perfect, and of course it isn't going to support every little niche.
Your concept that because of its open nature it should support everything from the history of gaming and computing is an unreasonable expectation. Old laptops work well so people who wouldn't otherwise have access to a computer can get something working for very little money, and because those devices are prolific. But even then almost all distros have deprecated 32-bit support.