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.
Well, obviously if you were jumping on and off the improvements look big, but as a continuous user of Linux since the late 90ties I can assure you that is was mostly a gradual improvement.
Sadly multiplayer compatibility due to anti-cheat is still a sticking point as has not improved that much overall.