I wonder what was supposed to happen in this chapter, but the manga didn't manage to depict it. In this manga chapter, Yuuto was single-handedly beating all the imperials, with none of them being his opponent, despite Yuuto not even using his full OP powers, by far. He could steal they skills with impunity. Yet suddenly he says they shouldn't pursue the humans because "they are better than us right now." Wut? In the novel the fight must have been quite a bit different for the dude to say that. Here in the manga he could have slaughtered them all without breaking a sweat.
It looks like he only killed that one punk. One punk in exchange for a number of demons killled, including small children. That shows Yuuto doesn't much care about demon lives either. I don't subscribe to the religion of edgelordism, but even according to the rules of traditional warfare (which I do subscribe to), he could have kept killing the enemies until they surrendered. After that, he could have exchanged the survivors for a ransom with the human empire.