I'm fairly certain that this has been the case in the past. I think i remember when wine was still very unstable some games ran better on linux than on windows. But the caveat was that some of the features were not translated via wine. For example some type of lightning or shading (as in shadows) technique... like you would just not have shadows. So back then it was said that games ran faster because the GPU did less work cause of the missing "features" when doing the translation.

Is this not the case anymore? Does proton translate all of the api calls from say dx12? Were the games tested in vulkan or dx12 and are we sure thy look the same visually?