There are tons of Linux games distributed on GOG, and not having to use a proprietary client is one of its great advantages. Not to downplay Valve's contributions (and I may well get a Steam Frame when they come out), but they mostly amount to porting their mandatory DRM-laden client to Linux, and maintaining a fork of Wine that integrates with that client.

Ownership, control, and privacy are among the main reasons I use Linux, and are likewise huge advantages that GOG has over Steam.

You're fairly significantly downplaying their contributions. They have a substantial amount of FOSS developers under contract working on SDL, DXVK, VKD3D and there's over a dozen people on working on KDE on Valve's dime alone. Proton isn't a fork of Wine, it's a Codeweavers managed project funded by Valve that packages Wine, virtually everything useful ends up going upstream given Codeweavers are also the main contributors to Wine. AMDGPU, NVK, Valve funded. Valve have been funding FEX since it's conception.

That isn't even everything, just what I've been able to confirm either through interviews or conference talks where their involvement has come up. They've quietly been doing a lot for Linux.

Official Linux releases are almost never maintained. I have the same game on Steam and GOG, but the GOG version no longer works. Neither does the Steam version, except if I switch to the Windows version with Proton. Then it works flawlessly (usually faster and better than the Linux version ever did.)