It is quite an acceptable situation and in no way weakens the OS. Typically, the IC is given a stronger role in films/screenplays because of the limited length of the work. It is easier to have the IC do multiple duty (the MC as well) in order to economize on time. That's why Archetypes appear so frequently. They are storytelling shorthand for potentially complex relationships. Longer works or novels have the luxury to examine a "passenger" IC to the fullest.