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.
The 10 developers Valve hired have nearly nothing in their Github profile. Proton history is nothing but community based code and a copycat of Wine, just like everyone said in the very start of Proton.