Ok, at least you got the definiton right (or at least you're closer, not applicable isn't exactly synonymous with irrelevent either).
But to your point, why should the team losing make me any less of a fan? There's something called loyalty. I'm a Bills fan through thick and thin...for better or worse. Would you divorce your wife if she gained a little weight? Would you give away your children for adoption because they pulled C's in school instead of A's? Would you ditch your country and move to Europe because you don't like a law that gets passed? No, because people have loyalty toward those things. I am a loyal fan of the Bills whether they go 0-16 or 19-0.
In other words, yes, winning is irrelevant to me being a fan. What is so wrong with being a sheep that cheers for the Bills? Isn't that what being a fan is all about? Fan is short for "fanatic" not "impartial observer".