Full versus empty isn't even the argument. Loads do not equal yield.
Just because there are more seats doesn't mean that a. you can fill them and b. a little more importantly, definitely doesn't mean you're making money on those seats. If that seems simplistic, it's only as much so as taking a full fare and multiplying it by X number of seats to suggest that much revenue as fact. Talk about a straw man: "But if you charge full fare for every seat and fill them all, why, it kills a 777!" Um, sure.
More seats are more potential revenue. But only a possibility, while the fuel cost is a certainty. If I was a gambler I know which I'd rather bet on.
Don't get me wrong. I enjoyed flying F on the ugly thing, it was comfy and it was always nice to say hi to all my colleagues along for the ride! lol Hopefully they'll see something other than a hangar again soon.