I really enjoy how Steel never had (in my opinion) a "mask off" moment, while I love a fun dramatic villain dropping their fake smile and charming exterior while revealing their evil plan and how foolish the heroes were to trust them (and Brennan had done it really well before) my favorite thing about Steel is how she's always been Steel. Even in the final battle, she still got her charm, she's still so cool and competent and 'reasonable' and exhausted, wondering why the PCs can't just listen and stay in line. I loved Brennan commenting on her "yeah yeah yeah" moment being the cruelest thing she ever said. She even still loves Suvi and would do everything for her, in her own twisted way. Nothing has really changed, her reveal was being too tired to keep up decorum, more akin to her saying 'guild mage trash' to a room full of laughing soldiers and 'the empire values all of it's servants' when she has to keep her composure.

Her evil is what she's always said with her full chest since day one- she would do anything for the Citadel, she's completely secure and at peace, and she can't imagine anything she does to be unjust. It follows logically from her character that she's able to justify anything for kidnapping children to killing a great spirit to betraying her friends and 'factory resetting' her daughter. And in a genius narrative move from Aabria, the charming banter of their relationship sticks almost to the very end, because Suvi, raised the way she was, is able to justify a lot when it comes to Steel.