Yeah team movies works with one character playing off the other. And hey talking about popularity, is Prof. X the most popular X-Men? Or the most exciting? Nope. But you have him there (and as the lead character in the latest movie which will probably be the biggest X-Men movie to date) because of his importance to the story and the lore. And it's getting the lore and the story right, then adding the more "popular" characters around that which is what makes a great film, cartoon or comic book.