I think it's probably worth pointing out that Brust is an ardent Marxist, and when he talks about societal stagnation, he is thinking about it from a Marxist point of view: he is saying the society has been forced to stagnate at a specific stage (feudalism, they've barely even reached capitalism in any meaningful sense) and can't progress toward the proletarian revolution that would be inevitable without the Jenoine's interference.

This comes up more explicitly in Teckla, when Verra is talking about Kelly: "Kelly has his hands on the truth about the way a society works, about where the power is, and the cause of the injustice he sees. But it is a truth for another time and another place. He has built an organization around those ideas, and because of their truth, his organization prospers. But the truth he has based his policies on, the fuel for this fire he is building, has no such strength in the Empire. Perhaps in ten thousand years, or a hundred thousand, but not now. And by proceeding as he has, he is setting up his people to be massacred. Do you understand? He is building a world of ideas with no foundation beneath them."

(One of the interesting things to me about Brust's books is that there is often a character who shares his Marxist beliefs, but he very seldom makes this character a particularly sympathetic one--in an effort to avoid turning fiction into polemic, I assume.)