@Kendama What are assumptions, besides him knowing further details being realistic and questioning the prisoners being weird to not happen? And your statement about his intentions of just being a war-monger who knew nothing was an assumption too, one that forgot that he has a spy ring and that for every action he's done we've been given more knowledge of, he has been extremely calculative (The SuWon visits the Earth Tribe arc was the first example of this and also the first in-depth look at his character beyond regicidal cousin, which from a story-telling perspective is a very important beat. The second time we get a look in his thought process
he waited ten years to stage a rebellion for multiple reasons; because a war for power right after Il had been crowned would have been bad for the country, because he didn't know what Il was thinking, and because Il hadn't ruled long enough to show if he could protect Kouka).
He may lean heavily towards violence to solve problems, but he doesn't do the violence willy-nilly, nor is he stupid.