https://en.wikipedia.org/wiki/Consent_of_the_governedLegitimacy is upheld by one of two things:
1. Physical skill (or magical power)
2. Cunning
Cunning gets cheap and dirty tricks done. And it does make a good ruler
if it is combined with actual benevolence, becoming wisdom. Physical skill allows one to hold power in a martial situation (the fear effect). But either of these depends on consent of the governed. If the person is brutal but they still don't care for them, that is loss of consent.
We may not like tyrants, but they are people who can hold their power because people fear them. Pretty much the sentiment straight from Machiavelli's
The Prince, which I gather doesn't exist in this universe. Plus, they know she is honest and decent so they also to some extent respect her, unlike this worthless snake.
Kinda like Aslan in Narnia, the White Witch kinda was good at tricking people, but c'mon Aslan was a freaking lion. Kinda a goodass (versus badass). Warden is tough as nails, but also pretty decent. And everyone knows it. Didn't even need to raise her voice.