That’s because I don’t understand your point. You complain about it being only for windows yet push away their efforts of bringing windows games to linux (which is proton). So indeed, the quality of proton is very much the point as it dictates the quality of the game on linux to a general extent.
Not to mention that this IS an early development build, I would say that its perfectly reasonable for them to only make the early builds for windows since that is where a majority of the play testers are likely to be (not to mention that linux -> windows tools don’t exist unless you want to game on WSL2).
So what are you trying to complain about? The fact that they aren’t exclusively pandering for steam deck users? If that is the case, I must admit that it’s very childish to just expect that and I hate other companies for making this the norm.