Been playing a lot of steam games with proton, it is mind bogling how valve expanded from support for linux for the source engine to support 70% of the games.
The giant youtube channel Linus Tech Tips has done a recent series of videos on gaming on linux. On Jan 1 they published a 15 min summary video that covers that 70% claim in a much more nuanced way: https://youtu.be/Rlg4K16ujFw
Punchline: it's kinda true, but there's plenty of struggle for new and multiplayer games still.
There are even bigger caveats to that number than what they mentioned in the video. Since all the ratings are based on user reports, there is no standard for what is considered a working game. You can look through pretty much any game and find positive reports that mention frequent crashes, performance issues, missing textures, requires a custom proton version, etc., but since it launches, they gave it a thumbs up. I've tried platinum rated games that are completely unplayable, ProtonDB ratings are a general guide at best.
ProtonDB also considers a game as "working" if even a single person gave it a thumbs up, so the big "17,984 games work" on the home page is very misleading.
It may be true, but it really depends on how new the games you want to play are. I don't consider myself a hardcore player, but I'm perfectly happy with the games I've got on Linux; Overwatch, Diablo 2/3, Warframe, Risk of Rain 2, the Fallout series... they all work fine. It's certainly no Mac when it comes to game compatibility. Really, the only time a game doesn't work on Linux is when the developers go out of their way to ensure you aren't running Linux; with the prevalence of anti-cheat that has indeed seen a bit of a fork in the road. But developers can also whitelist Linux users, and now that the Steam Deck is getting ready to ship to hundreds of thousands of future owners, those devs have an incentive to get their games on Linux.
I think "asterisk" is warranted, since there are still show-stopper games that won't run without their precious kernel-level anti-cheat (sorry professional Valorant players), but the asterisk is shrinking, not growing. It's a fairly small caviat at this point, especially for more casual audiences, and I kinda wonder why it was such a sticking point for Linus. Wine is not a panacea, but if you look at the landscape and see the majority of Windows software running, I think there's hope in that.
I am sure it heavily depends on the kind games we play but I've had a 100% success rate over the past couple of years. I have to keep reminding myself to check protondb just in case. There are even a few games with native ports that I run through proton to avoid bugs in the native versions.
That's what's making the Steam Deck possible. And the release of the Steam Deck is only going to bring more attention to Proton and accelerate further development.