Yes call X is faster than call Y in Proton, but that could also be because its only 50% written and skips a bunch of side effects that will be created after you have written your game.

Therefore you need to view Proton as a potential moving target. Not that Windows isn't too, but its just not as clear cut as is being claimed.

I know this because I pin some games against older versions of Proton because they work better/faster.