Ah, superhero teams. Even more so than individual superheroes, they’re tricky and the most subject to the inherent flaws of the big two comics model. I’ve entertained one team of superheroes, and it’s tricky, especially the bigger the hero team becomes.
I think the Fantastic Four, and to a lesser extent the X-Men, are the way to do a superhero team right. They’re (to an extent in the X-Men, and definitely in the FF) built from the ground-up as part of a team from the get-go. The Avengers and Justice League are the way to do it wrong, taking existing solo characters and stuffing them into an inherently artificial team (see this Spacebattles post by “Unhappy Anchovy” for a similar view).
To use a sports analogy, the Fantastic Four are a proper team. The Avengers and Justice League are an artificial all-star team.