@seiaxen Yes I read the previous chapters, but nothing in there would make someone automatically braindead. Being an assassin doesn't mean you lack common sense or all social skills. He wasn't treated like a child soldier, as in reduced social stimulation and taught to lack empathy. He was treated as a son, had relations with other people his age, and was not kept in a bubble. He had more than enough opportunities to develop into an individual that possesses common sense. I'm not saying he is the most perfectly well-rounded individual, but he was not put in a situation that would kill his empathy and logical reasoning. He specifically said that he HATES when people make empty threats, meaning he has been in a situation where he has been attacked while the opponent was not bloodlust before. He was wondering why the noble was holding back, when he himself was also holding back. If MC just opened fire and killed him, because that's how he was raised, THAT would be more consistent with what you are saying. But since he is also holding back, since he knows killing people in broad daylight isn't a good idea, he should also know that same rule applies to other people as well. Not making the connection that something that is bad for you is also bad for someone else only shows that he is stupid.
TL;DR: The dude should be able to understand that killing someone in broad daylight is a bad idea, since he knows it would also be bad for him to kill someone in broad daylight. Since the MC knew he had to hold back, he should be able to understand the reason why the noble also had to hold back. Since he cannot understand why, he is dumb.