Fighters are much stronger when there are no rules

If the goal is to kill without rules, it would be no trouble at all for Ngannou to immediately strike the windpipe and fracture the neck bones to kill someone.
Kicking the groin, smashing the vital spots..
The only reason people don't die is because all of that is prevented by rules, and the referee steps in the moment things look like they might go wrong..
If special forces operatives fought barehanded, Ngannou could kill them in 10 seconds with just one strike to the windpipe.