In that first day, the Duke did fall for Keisha's "spider" tactic. Without Shin awakening his own insticts and personally making his move, the rear had been put in a very bad spot and Duke Hyou's army would have lost 20k men like Ten said. Given that it initially was 40k vs Zhao's 120k, this would have been a fatal blow.
"At this rate, the Duke Hyou army will be defeated right after the battle of Kankoku pass begins.".
But Duke Hyou is nonetheless a superior instictual to Keisha, like Riboku admitted. The difference between them was clearly evidenced when the Duke was able to read Riboku's origin tactic, which Keisha had outright failed to accomplish. Riboku, who previously considered Keisha to be the most terrifying instinctual commander, had to come back on his words and crowned Duke's feat as something unthinkable. He didn't even believe a strategic type would have been able to read that shit, let alone somebody with insticts.
The Duke reading that tactic has easily got to be one of the feats that most impressed Riboku in his entire career. Ousen cooking up a succesful plan in a literal few hours to deal with the untakeable Gyou, something Riboku said "to have never heard of", is another.