"If you want to go to an easy high school so it doesn't interfere with your budding career as a manga-ka, as is the case for Takagi, then at least seriously consider the pros and cons. Don't study just because it feeds your ego. Don't go to a good college just because everyone says it's the "proper" thing to do. The important thing should first and foremost be figuring out what you want and how to get there."
Your statements there applies more to Azuki than it does to Iwase. Don't become a seiyuu just because everyone says it's the "proper" thing for a girl to do. Don't try to be cute just because everyone says that's what girls should be like. I respect your opinion that being happy is more important than being the best, but not all people feel that way. For Iwase, it seems to me, being the best is what makes her happy. And so I don't think your argument really stands in this particular case.
As for her not being satisfied with her life, I feel the fact that she's still chasing after Takagi is more indicative of her obsessive love for him and that she is pursuing her goal of surpassing him, in the same way Azuki is pursuing her dream of being a seiyuu. I don't see why going after your goals should necessarily indicate that you're unhappy.
If anything, it shows that Iwase is very clear on what she wants and how she's going to go about achieving it. In school: get better grades than him. In college: be a better writer than him. (And she succeeds marvelously - winning a very prestigious competition, gaining some fame as a up and coming young writer). And then once she finds out he's doing manga, she does it as well to surpass him. So I would think, yes, Iwase knows exactly what she wants and how to get it. And she's succeeded, hasn't she? Natural is far better than Trap ever was.
And precisely because she's so talented, the creators can't allow her to be a likeable/decent person, because that would go against their misogynistic ideal that "girls who show their intelligence are stupid and uncute". Look at Aoki. In the beginning she was portrayed as a genius writer and an arrogant bitch. After character development etc, she becomes nicer and cuter... and look how the portrayal of her abilities changes with it. Her new manga succeeds only because various male characters are helping her with panty shots. And the focus is more on her subpar art compared to her storytelling skills.
"As for the fact that [Azuki's] desires happen to be stereotypically feminine, well that's just a coincidence."
That's not "just a coincidence". Takagi is praising the fact that her desires happen to be stereotypically feminine. He says over and over again that she's not being "calculative", that she's acting in this way because she's just "being a girl" and because these are girlish things to do and want. He is praising her TALENT for naturally having stereotypically feminine desires. In short, he's saying that she's smart for conforming to society's expectations of females.