They missed a lot of opportunities primarily because they have SEVEN main characters to focus on. It gets hard to flesh them all out and keep the action moving, ya know? I like Yamaoto, but I wanted to see other characters too.
Kyoko knowing about the mafia but being cheerful for the guy's sake would have been far more interesting to watch. Haru could've been ditched right from the get go. She provides literally nothing to the story.