Not arguing with you on the overall point, John, as you're right on Knoxville's career versus Rock's, but Rock did lead The Scorpion King, which did in the same ballpark as the The Game Plan domestically, and was even better in foreign theatres too.
Like I said, you're right on the overall point, though. After The Scorpion King, though, any movies he was the lead in were in the $30-50 million range until he did The Game Plan.
Scorp was a spin off from a movie that pulled in $200M, coming out just one year after Mummy 2. It was heavily pushed as such, and one can even go to Box Office Mojo and still find it listed as part of the Mummy Franchise.
One could reasonably argue that the "lead" in the movie was the Mummy Franchise. That was kind of obvious when Rock's next two movie made about half as much money.
I'm not one who craps on Rock's career. I'm glad he got out of wrestling reasonably sane and is making good money away from it. I'm actually pulling for him to have a strong career, and find his breakthrough to an even higher level. Just have to be honest that his box office has been pretty pedestrian over the years.
John