The quality of Proton is not the point, the point is that they’re not dogfooding their own platform. They’ll likely follow the same course as CS2: Lengthy prerelease test exclusively on Windows, then a few days before actual release someone will port the game to Linux/SteamOS and release day is the first day of the Linux port’s alpha test.
How can anybody at Valve expect game publishers to take Steam Deck and SteamOS seriously if the developer of the actual platform is not dogfooding it with their own games?