Source is this video:
Windows Was The Problem All Along - Dave2D
We could obviously compare performance between windows and steamOS before on the steam deck, or between windows and Bazzite on other handhelds. But this is the first time we have had official windows and SteamOS builds for the same hardware.
Why? Valve has been sponsoring all these projects for a really long time. While wine existed before that, it wouldn’t be anywhere near the shape thats its currently in because gaming was not its main focus. There have been loads of gaming bugs and sharp edges that have been around wine for a long time until Valve put in the money and devs to fix them.