Power is central to a comic book character’s success. It defines who they are and what they can do. And, more often than not, it gets way out of control.
Characters can easily become so powerful they become boring and indistinguishable. Maintaining a story where there are “levels of power” (i.e. this thing is more powerful than that thing) is critical to making team-oriented stories work. If someone can never be defeated then there’s never any “real” jeopardy they can be in, which means the audience can easily tune out.
“The Avengers” keeps everyone’s powers in balance. In a movie where everyone can be the best, not everyone is. In a movie where everyone can be a god, not everyone is. Some people were strong, others were stronger and a few were the strongest. And everyone’s individual strengths remained distinct.