If you start with three heroes (Charlie's Angels) you end with three heroes ... if you start with one, you're best to end with one. Otherwise, you run the risk spreading the focus from one central character to others that don't matter, in the end.
Another example, the first
Star Wars {a/k/a Episode Four}. The hero? Luke. Who triumphs at the end? Luke. Han and Chewbacca help, especially at the end of the Death Star Trench sequence, and Obi-Wan is there
in spirit to guide Luke, but it is Luke that must feel the Force, use it, and fire the proton torpedo at precisely the right moment to have it sucked down the thermal exhaust port.
As an aside, I've always wondered... if they have to fire a torpedo into a port that is flush with the skin of the Death Star, then why didn't they come at it from space? Firing at a target that you're pointed at is a lot easier than trying to have it curve into the port.
Of course, that would have eliminated the need for the whole trench sequence...Al Bouchard