Proton didn’t exist in a vacuum though. It existed for Valves previously failed vision of the Steam Machine. Those were actual product lines that existed (briefly) to go along with Proton.

The Steam Deck was Valve finally getting sick of nobody doing what they wanted, and technology getting to where they could do something more interesting than just another desktop.

Proton came well after the steam machine failed. It was plan B.

I could have worded it better but that’s my point. It was sort of their third attempt to make Linux gaming a thing (steamOS 2 + proton) before they finally came up with a compelling product of their own.