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.
At least initially this was mostly DXVK though, which is a project that was secretly funded by Valve after it showed some promising initial results.
as someone else said, it’s a “standing on the shoulders of giants” moment for Valve