Again, generalizations like "serious gamer always does that" are not helpful. Lot's of people are not satisfied with Windows for many reasons. Would they switch to Linux if they could play their games? Many would and already do, and I wouldn't call them not serious.

Performance variations are not uniform. I.e. it's not a given that Linux always reduces performance. Proper made games actually perform better on Linux. Of course if you are using translation layers like Wine, some performance hit is expected to compensate. That's not necessarily a bad trade-off for those who want to switch, as long as result is well playable.

> If it were a natural fit, they'd be interested in using it.

They are, increasingly.