Even gamers nexus’ Steve today said that they’re about to start doing Linux games performance testing soon. It’s happening, y’all, the year of the Linux desktop is upon us. ᕕ(ᐛ)ᕗ
Edit: just wanted to clarify that Steve from GN didn’t precisely say they’re starting to test soon, he said they will start WHEN the steam OS releases and is adopted. Sorry about that.
The marginal extra disk spaces used by flatpak really isn’t a concern for most users, much less valve. If you do everything in flatpak and your apps only use current runtime versions, the additional space used by flatpak is in the megabytes, since libraries like libc are going to be on your host no matter what.