Never said they would win a straight up fight. I said I think that Xykon becoming a god through Roy's doing (which, if Roy could make people gods, would be an odd choice for him to use his rather insane powers on) would make large swaths of the story so for irrelevant. Not to mention the entire theme of systemic injustice in the world, to boot.
It's not a binary choice of either your theory or them hitting Xykon and Redcloak with a magic sword. Other options exist. I strongly suspect the answer is one of the other options, even if I don't know what it is.