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.
To add to that, back in the day you had to find out what engine a particular game used as there were huge compatibility issues with certain engines and others ran a fair amount slower via Wine. Some engines, however, ran incredibly well under Wine.
That said, there were some cool things you could do in Wine like define a pseudo monitor to run your game on. Example, back in 2010 (before widescreen monitors were more common) I had a triple head setup on Linux. I could specify in Wine an arbitrary monitor size (like say 2560x1024) and run games “full-screen” centered on my setup while having other windows open on the edges of my real desktop.
Even games that officially didn’t support multiple monitors and on Windows (would force themselves to one screen and black out the other ones) ran well via Wine with this setup.
It was a bit involved to get working the first time though!
Played through the HL2 games, Supreme Commander, Rift: Planes of Telara, and even Wow that way (though WoW had other issues with non 4:3 displays).