That only grants market control so long as Microsoft keeps releasing new APIs, otherwise the people reimplementing them like valve/wine will catch up.

I think Valve’s play isn’t to steal tons of Microsoft’s gaming market share; their play is to just get enough of a market that game developers are incentivized to code to the APIs that work well in Proton, not whatever the latest and greatest in Windows is. If we cross that inflection point, Microsoft’s PC gaming chokehold will be on life support.