I'm not sure how they could have failed that if that was never their goal in the first place. The entire point of Proton is that the Win32 API is infinitely more stable and worthwhile to target than anything Linux distros offer, and that the financial incentives aren't there for developers to 5x their platform distribution effort to reach 1% more users. An approach that relies on developers doing that would never work, and fortunately for Valve that isn't their approach.