In 2017? Well, that's an interesting question. On one hand, it definitely wasn't as easy as it is now. On the other hand, I was motivated to ditch Windows and willing to make the gaming sacrifices necessary to make that happen. The last version of Windows I used was 7, and I was determined that 10 would never touch this machine -- or any computer of mine going forward, for that matter. I also was done putting up with 7, given that Microsoft was starting to backport 10's spyware and forced-upgrade BS to it by then.

It's been a while, so I'm fuzzy on the details of what I was playing between 2017 and 2018 (when Proton came out). I think I just limited myself to the subset of my Steam games that had native Linux versions (e.g. TF2 and other Valve first-party games, Don't Starve, Cities Skylines, etc.), supplemented with PlayOnLinux for Star Trek Online, which, being an MMO I was already committed to, was pretty much the only exception I made. Otherwise, my attitude became "if the developer can't be bothered to support my OS, that's their loss, not mine, and I don't need their shitty Windows-only game anyway."

After Proton came out and I flipped that switch to "enable Steam Play for all other titles", I think the majority of my Steam games "Just Worked" -- yes, even back at that initial release -- and the ones that didn't became compatible pretty rapidly over the next couple of years. With one exception, I don't think I've had trouble getting a game working since the start of the pandemic, if not earlier. At this point, I've softened my "I won't buy a new game if it doesn't natively support Linux stance" and instead simply expect every game I buy to work. And they have!

(That one exception was Star Trek Online, which I had continued running via PlayOnLinux because (a) why mess with a working config, and (b) the Steam version of STO wants to permanently link your STO account to your Steam account, which I didn't want to do. One day, though, they updated the launcher or something and it quit working. I eventually gave up trying to fix it in PlayOnLinux and decided to use Proton for it instead. But I still didn't want to link my accounts, so I had to jump through these weird hoops where I installed the Steam version, but didn't log in or play it, and instead re-imported it as a non-Steam game pointing at the executable for the Steam version and then fiddled with the compatibility settings to find a version of Proton that worked. That's still the configuration I'm using for it to this day.)