Well I mean such data does exist, or easily could, assuming its possible to just turn on an FPS counter in a game on a Mac, or overlay one, and I don't really see any reason why it wouldn't be possible to run at least basic benchmarking on the same game on Win/Lin/Mac.

Many games just do those things inside themselves in either a benchmarking mode, or have a console command that will display basic info like FPS.

I don't have a Mac though, and Mac users broadly don't appear to be interested in even basic benchmarking.

But also haha no I would not be surprised that using a KVM switch is generally a giant goddamned hassle and its generally easier to just have a few devices you move around, I have discovered that as well!