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.
Personally I feel what it gave them - primarily - was the ability to be independent of Microsoft, not beholden to them in any way whatsoever, and not having to pay them any license fees.
The fact that after putting so much work into making Proton and that whole toolchain amazing it actually turned out faster than Windows, well, that’s juat the delicious icing on the cake, from a commercial perspective.