I’ve found that it depends heavily on what game you’re playing. I wouldn’t say 20% loss is uncommon.

You could try using a kernel tuned for gaming but it probably won’t make up the difference.

Honestly you’re probably better off not comparing to Windows. You’ll often fall short performance and feature wise.

Edit: I’ve also found that people tend to oversell Linux. We desperately want more users but exaggerations do more harm than good.