Maybe you know this, but steam does more than get games playing on Linux. They (Valve?) have a group that develops drivers for AMD gpus on Linux. Their contributions still may not ve limited to just that primarily, but if there wasn’t Valve it would seem we’d have a lot less to play on Linux at the very least.
A lot of their work on proton also gets upstreamed back into wine, so even for those not using proton, they're still benefiting quite a bit in recent years from all of the work Valve has done on that front.