They don't work properly. Things like alt-tabbing out of the game crashes the game for example, or performance with streaming is utter shite. So it doesn't run fine.

The few games I have native linux ports for, I can alt-tab out of and I get consistend performance.

I know they don't, that's why I wrote "if". I wanted to express that I don't see the difference between a perfectly fine native Linux proprietary build, and a perfectly well executed, proton-backed user experience. I think I get what you're saying, that currently Linux builds behave better than whatever proton can provide, and I agree.