Genoise vs whipped egg whites - which makes cakes fluffier?
Génoise is always made with whipped white eggs for maximum fluff. No matter how long you whisk your whole eggs, they will never get close to the consistency of whipped egg whites.
Found an interesting comparison video here: https://www.youtube.com/watch?v=YCdOU-1sjO0
Now if you make your cake with foamed eggs I'm sure it will be good, but it won't be a génoise anymore.
Regarding the use of butter, there are two schools, some use a bit of melted butter, others don't use any butter at all. I personally never use butter because I think it is lighter and fluffier without it, and generally I fill my génoise with ganache, so that brings the fatty element to the cake. However it is always melted butter, I have never seen a recipe using creamed butter, and indeed I think it will make your batter heavier and your cake will be denser.
But if you ever try please let me know!