Kou En’s title is “the conqueror of the East”. All territory in Eastern Chu was literally southern Qi 20 years ago. So it’s highly likely that Kou En conquered the entire southern half of a super state.
Now recall how much trouble Juukou alone gave Tou, Moubu, and Houmei…
And then imagine Kou En conquering dozens of Juukou’s by himself. lol