They should be more scared... Mac, ChromeOS and Linux now have roughly 1/3 of desktop/laptop users. Linux having gained a lot of ground just this past year, and IMO Valve is probably solely responsible for most of that.
Even with the Valve store cut as high as it is, and some of their sketchy terms... they've been far better stewards to gaming than MS has been to Computing/OS.
Not even close, still around 70%.
https://gs.statcounter.com/os-market-share/desktop/worldwide
70% is by most measures, pretty close to 66% (2/3)...
It is all a matter of number engineering, after all, as by the old account tale, which got hired because it answered correctly the interview question with "what do you want the numbers to look like?".
Outside countries like US, and similar economically level, Apple desktops will never be a big presence, unless they change their premium price policies.
On the same markets, hardly any normal person can buy GNU/Linux desktop/laptops on regular computer stores.
Their choices are between Windows, ChromeOS and Android tablets with detachable keyboards, which naturally makes most pick Windows regardless.
And for most people, computers are just accessories like the wall clock. Even for people who work on a computer all day don't care about it as long as they can do their task.
Agreed, and those wall clocks will keep running Windows for the foreseeable future, even if they get out of rythm every now and then.