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 quantum leap for linux gaming was that one guy who wanted to make nier automata work and developed dxvk.
I would probably agree to that more than for Proton, but the truth is also that DXVK’s further development was largely funded by Valve.