I really don't get what people are complaining about.
He already won. His decision to hand him to authority occurs after the guy got incapacited.
Wanting to kill at that point is just being edgy and paranoid rather than being rational.
Like, what, you think everyone trying to kill you always got connection to the underground and controls half of the world? Who are you, center of the world? The protagonist of some isekai manga?
Handing him over to be imprisoned while MC and the authority takes their sweet time getting any info from him is the most rational action, and it does half succeed since the dude now got no hand, normally enough to prevent him from taking action, if the bleeding doesn't kill him.