From what I understand, it takes more contrivances for the Avengers to take this home. Flash's speed goes unanswered, as does Martian Manhunters telepathy. The consistently superior strength and speed of the Justice League puts the Avengers on the defensive where they can't win from. They'd need the Justice League to forget many of their abilities so Iron Man would have time to pull together something, and Wasp time to go sting somebody's brain, and Scarlet Witch build up an epic effect. Justice League, assuming writers don't have any particular goal/story in mind.