I really like this arc. You see "The genius teacher" overriding "The normal teacher" in plenty of sports/shounen manga, but the normal teacher in this case is completely correct in his expectations. A 15 year old genius is still a 15 year old. I respect the characterization of all 3 of them a lot -- none of them have done anything objectively wrong. Iwai-sensei wants him to spread his wings, Nakamura-sensei isn't trying to constrain him so much as keep him on the perceived path of correct development.
Normally you'll see the genius artist win out in a matter of chapters, so I like that there's some torment here. Being 15 years old is hard, after all.