As a linux gamer and enjoyer of windows v linux benchmarks you cant say windows is often worse thats just a straight out lie. Rarely is proton "better" than windows. Proton is usually about 10% less avg fps than windows. Its is closer in 1% lows and wins more often there.
AMD, Nvida and intel I watch benchmarks for all GPUs. AMDs are the closest to their windows counterpart but its still around 10% roughly speaking. Keep in mind this is without ray tracing. If thats enabled linux is like 30% worse.
Nvidia is getting better I think they merged something recently that will help their vulkan pref match windows.