There's still room for improvement, but Linux gaming has come a long way in a short time.
I remember when Proton launched it was like magic playing games like Doom and Nier Automata straight from the Linux Steam client with excellent performance. I do not miss the days of having the Windows version of Steam installed separately.
Proton is not an engine, it's a compatibility layer and thus would decrease performance compared to native. However, sometimes it's still faster on Linux because it has less overhead.