Has it really been that long? Apparently so. Valve originally announced their rebranding of Steam Play with Proton back on August 21st, 2018. Seems like a good time for a quick reflection being halfway to a decade old now with the tech that gave rise to the Steam Deck.
It's a collaborative effort. The Wine and Vulkan projects have all done a lot and deserved credit for doing massive, amazing things. But for Linux gaming specifically, Proton has absolutely changed the landscape, and if Valve continues down this path, will make Linux an ever better gaming platform. So I don't think it's unfair to say thanks to Valve.
Not only have they sunk significant resource into making Linux gaming more viable, they've released Proton under BSD and seriously pushed developers to make Linux-compatible binaries. If Linux continues it's slow upward trend in popularity, Valve will be in large part to thank.