Methodological issues aside, I don't find this result surprising at all. I expect this result as someone who has gamed exclusively on Linux for years now.

On the Valve side, SteamOS is about as close to a purpose-built gaming OS as you're going to get. The Proton compatibility layer works so well that some games perform better on Linux than on Windows -- I assume this must be due to unnecessary Windows overhead, but can only really speak to the result.

Nitty gritty aside, I think the key issue holding back Linux gaming now is adoption. It's free. If you haven't tried it, try it.