Hold up, how is proton leveraging open source to avoid dev costs? Are you referring to steam using and contributing to existing projects instead of reinventing the wheel? Or to game developers that use it as a reason for not making native Linux versions, which wouldn't be Valve's workforce in the first place?

I can see how the things Valve does contribute to their business model - steam input giving their controller compatibility with games, proton letting them launch a Linux-based handheld, and the new recording feature probably there for the steam deck... But the thing is, Valve is still providing all those things to customers for no extra charge, and they keep adding new stuff.