MI5 was the 6th highest grossing film of 2015 mainly because of Tom Cruise's stunt work, and his movies all make at least 2X its budget, so I don't know how he doesn't have star power. Will and Tom have far more box office hits than Brad Pitt.

Well Mission impossible 5 was also one of the biggest movies of 2015 due to Tom's ability to do his own stunts, so I wouldn't write him off yet.