How The Switch Would Fix It:
Mark Wahlberg has a voice that sounds like someone put every accent in the greater Boston area into a blender and then sprayed the pulp through a fire hose. In short, it's great. His expressions, on the other hand, especially the ones he needs to pull off in dramatic scenes, leave something to be desired. He has less facial dexterity than a piece of Tupperware, so by all means, we should be trying to hide it under something. And that something is built into the movie. Under the ape prosthetics of Colonel Attar, Wahlberg could focus on his greatest strength, which is snarling at everyone in the room.
This would leave Duncan as the human captain, which is the most "duh" casting decision in history, because Duncan can play any role you need. He can be the toughest guy in the room (Daredevil), he can make you laugh with his stupid antics (Armageddon), and he can turn you into a teary-eyed mess as you witness the persevering humanity behind his imposing stature (The Green Mile). The man was one of the most underrated actors in history, and it's a crime that the creators of the Planet Of The Apes remake saw him and thought "Yeah, he's nothing but a mountain of pecs. He'll be great as an underwhelming ape colonel." Giving him the human role would allow him to flex his considerable dramatic (and muscly) muscles, and it would also give him the chance to wear a loincloth, which is a win for everyone, really.