Usually, the most impressive competitor to a Microsoft product is the most recent prior version of that same Microsoft product.
Windows 10 is still the biggest competitor to Windows 11 in raw numbers, but I'm pretty certain this is the first time in Microsoft's history that its most impressive competitor was the *FOURTH* most recent prior version, Windows 7.
That makes surprising sense to me, because 7 was current when Steve Ballmer bonged an iPhone and saw Windows 8 in that high.