I don't think that killing people is in the best interests of those in power
Neither is it in anyone elses best interest!
The world suppose to be like this, everyone in this world goes duel to the point to leave one worthy human to survive, which fits the narrative of how social natural animal does. They fight for a deathmatch and only the one who is superior and strongest survive and deserves to live in this world.
Your understanding of human behavior is not accurate. Animals generally don't kill members of its own species, unless the member is a threat to the group. Humans have continuously worked towards larger and more stable groups. It's more efficient and a lot safer. Even when a strong warlord comes around (and they too are not alone), they don't stand a chance against organized countries.
Duels where not a rite of passage or anything like that. They were ways to once and for all solve conflicts.
This means that before effective policing where in place, you had the right to challenge the opposition to a one-on-one duel. This as a more civilized alternative to tribe wars - cycles of murder and revenge.
The only reason violence is still around is for the simple fact, that you cannot counter violence without using violence yourself. If I attempt to beat you up and take your things, violence is the only defense that can be deployed without my consent. Instead of the option to challenge me one-on-one, modern countries give you access to a police force which easily overpowers any one individual.