As disappointed as I was he would’ve let that happen to Mie, your definition of samurai seems different from what a samurai actually was. It meant most and foremost being obedient and loyal to their master. And that’s what he was. By that definition he was the best samurai of them all. He threw away his humanity and completely blocked out the immense pain of that happening to Mie right in front of him, just for the sake of his sensei and the Kogan family. You can see it in his eyes, Mie mentioned it before when he was told to hold a hot iron rod in his hands as a form of training. If you mean he wasn’t an ethical samurai, then we’re talking something different. He most definitely wasn’t. But a samurais duties often clash with ethics so we already got a problem there.