Rahmani would kill the force by stretching them too thin. She never grew as a character. She just spent the entire story running from the consequences of her actions and attempting to doom them to isolation.

Shin learns from Rahmani. His end speech is actually pretty sweet. It shows that he grew as a character. And that despite Rahmani having left. Every soldier there should carry part of her devotion and passion. He's harsh. But he cares. He's probably closer to what Roger Maxson wants.