In my playthrough when push came to shove i had Ian ultimately toe the line Minerva wanted (as much as he hated it) because of pretty much what you say; it was the most pragmatic, "adult" move that seemed to fit Ian's default character. Even switching reviews, while an appealing option, carried a risk of Minerva taking it out on Holly afterwards, and it didn't seem to me Ian was selfish enough at that point to take such gamble without player's push.I replayed ORS earlier this week with a playstyle where I try to play based on the informations the game gave me about Ian and Lena (so far during each chapters).
And while controlling Ian in early chapters, I feel that it's really hard for me to make Ian be defiant in his internship place towards Minerva.
I think this is why the defiant move earns a willpoint -- because it's something out of Ian's comfort zone.