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.
Sure, but they are comparing SteamOS, which is a stripped down OS that does not have all the capabilities of a full Linux OS.
Just try using any photo editing software on SteamOS. Even ones compatible with Linux.