> if their old steam OS version even integrated Proton properly back then.

"Proton" wasn't even a thing that existed back then :)

Wine was a thing and you could run quite a few games, but it wasn't integrated at all: you had to run a separate win32 Steam instance under wine.

Indeed, and as a person who always wanted to game on my Linux boxes, it wasn't (still isn't) nearly as good of an experience as Proton, even though Proton is just Wine+patches+other goodies.

> you had to run a separate win32 Steam instance under wine.

If I remember my trying days during that period, all the Steam games you ran that way (unless hacked around) also shared the same Wine prefix, with all the fun stuff that comes with...

Indeed. Having to share wine prefixes (or having multiple Steam installs) was a problem. I don't think I bothered running more than a game or two.

Proton also include DXVK and VKD3D which weren't a thing at that time (Wine had ok DX9 support, awful DX10/11 and non-existent DX12).