Valve is doing god’s work when it comes to Linux gaming. I have played over 40 hours of GTA V without many troubles. The game looks great and performs great. So glad I could get rid of my windows install.
I think that the only gaming company that actively improve Linux gaming is only Valve. Compare this to Stadia, where I never see any news on them contributing to the Linux gaming stack
I would also assume that by getting devs to port their games to Linux to run on Stadia, the contribution may be more indirect. You'll get more game studios contributing to the stack, even if Stadia themselves aren't yet.