An entire third, or zero. Other numbers don’t exist. Valve obviously needs every cent they take, to do the bare minimum you smugly rub in my face, as though I’ve never even heard of their service. All that value just goes right back to the game-makers! Aaand all the hardware research and development they do for themselves but nevermind that.
And I guess GOG is a clear counterexample of your own point but uhhhhhh smokebomb!