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.
Not to belittle their work, but the majority of stuff that made up proton wasn’t theirs back then (basically wine+dxvk did the heavy lifting). They owned up to it in the end, paying driver developers and hiring dxvk authors and if I’m not mistaken also fund some wine work. A rather successful open source story but they aren’t the initial driving force.