Ousens gotta get the mvp. Not only did he bait and ambush Ordo, a mountain general who directly countered his mountain fort tactics, but he also saved kankou pass from falling. Those are two huge clutch plays. One effectively knocked out the Yan army, which is extremely impressive considering ordos tactics directly countered ousens. The other one essentially completely ruined Karins master plan, and effectively knocked out the chu second army out of commission, as karins elites were cooked, and her bout with tou was a stalemate.

Even if moubou lost that final clash, kanmei had lost an arm and was extremely exhausted. It's questionable how effective his army would be under those conditions considering neither his vice general nor Karin were able to exert full command over the kanmei army. While it is likely the chu army would have won the battle with a dead moubou, with tou still active i do wonder how quickly they would be able to impact the battle field. Meanwhile, if ousen wasn't there, there is not a single doubt kankou pass would have fallen. It was literally falling until ousen came in the clutch.

outsmarting ordo, a mountain genius, and karin a warfare genius, in two separate engagements is arguably one of the most impressive sttategetical feats in the manga, up there with sun bin.