Protondb isn't completely reliable, it's all based on user generated reports of how well a game works. I've had games that were rated gold and platinum on ProtonDB fail to launch on my PC. Then you have people reporting that a game works great, but they say that they had to compile a custom version of Proton, not just use what's included with Steam.
Honestly, it has never been easier to get a version of proton that makes gaming on linux seamless. Of course, I understand "run these terminal commands" is the usual defensive linux nerd^H^H^H^H coward's reaction, but installing Steam and this package from flatpak and then going from there is a _vast_ improvement from yester-years. I've been fairly happy with it, and I didn't have to do any actual compiling / building!
It runs many more games than the Nintendo switch right from the start, with many people being able to play games on the go without buying them again.
It's not perfect, but it sounds like a much better deal than the Steam Machines which didn't really offer any additional value to anyone and were much more limited.
That's the problem proton does not run all the games.