From what it sounded like and what we've seen so far, Shiratori isn't a bad author or a bad artist at all. His problem was always a lack of confidence, due to his mother. His sister and father's endorsement got him partway there, but he still needed a boost. Shujin spent all that time psyching him up to it, as well as giving him a few points here and there. He forced Shiratori to realize he is a strong mangaka in his own right, and always has been.
The bonus of this development was we got to see plenty of Kaya being cutely worried. These last few chapters made me like Kaya more than ever.
Iwase is great. She so obsessed with Shujin that she makes really rash decisions and hilarious overcompensations. Her "rival" has found success in manga? Compete as a mangaka! He's found happiness in love and that's made him a better writer? Try and snag the nearest man! She has become one of my favorites because she's so out of control.
She makes the rest of the side characters look remarkably sane.