But the issue is that it is many multiples of that, especially on the most common PC gaming hardware (Nvidia GPUs), often more than a 25% difference in framerates. Not so important at 144fps, but very important at a 60fps baseline and for genres like fighting games.
A lot of people don't mind, say, an extra 5 frames of input delay. They don't notice it. But a lot of people do notice even an extra 2 or 3.
I do think that frame pacing issues kinda do have a critical thin threshold where it's either bearable or an unacceptable difference. And the native windows version can often already be riding right on that line. So while it's not fair to the Linux version to demand better, it is unfortunately the case that it might tip over that line.