Richie Roberts' stories slow the film down

American Gangster interwove the stories of two characters -- Frank Lucas and Richie Roberts, each played by Denzel Washington and Russell Crowe. Since they are the antagonists, it's understandable why the director put two characters' stories one after another like a many-layered sandwich. But every time Russell Crowe comes on the scene, the story is slowed down. Especially Russell's side-kick detective adds little to the story. Some scenes seem totally irrelevant, like the side-kick's incident in the black neighborhood. Why is that story even included? Also Richie's divorce proceedings don't interest me at all. Richie's story isn't as interesting or dramatic as Frank's story. Since the title of the movie is American Gangster, it should focus on Lucas, not Richie. I felt like separating Lucas' stories from the movie and watch them separately from Richie Roberts. That would make the story much more interesting.