[quote=@Doc Doctor]
<Snipped quote by MelonHead>

I'd imagine a straight shot to the jaw would take even a trained fighter down if another trained fighter of equal skill delivered it (note how I didn't mention how said opponent would handle the punch, as I'm not actively trying to reason out how one character can evade or alleviate the damage of a punch, which is a whole different matter), in a reasonable roleplay. I'm not talking about pure skill and how it can change the tide of battle. Skill is an assumed constant. That's just one scenario one that I proposed initially. The addition of armor changes the circumstances. Regardless, a blade through a joint can end a fight as quickly as a blow to the jaw. Superhuman characters tend to be able to tank what normally would be lethal otherwise, via enhanced durability or other means. 

[/quote]

Your point was that a fight is over quicker at lower tier levels, though if you believe that because you can physically disable a human by delivering a super precise and powerful blow, that's faulty reasoning. A human being could also be disabled very quickly by punching them as hard as you can in the throat or being kicked in the bollocks, but the likelihood of a blow like that landing clean in the first few seconds of a fight between two roughly equally skilled fighters who are aware they are fighting is almost non-existent, especially in the narrative format of an arena fight.

Besides which, there are plenty of examples of non-super-humans (unless you believe Shaolin monks to be superhuman, which is perhaps a matter of debate) taking blows exactly like that without being incapacitated. The danger of a blow of that kind is that it rocks the brain in the skull, rendering the person unconscious, but it is never a sure fire knock out. In fact, it rarely is at the higher levels of combat sport, unless the fighter in question is one with a 'glass' jaw. Its notable enough (being vulnerable to that sort of strike) that there is a name for it, and therefore a high likelihood that some people are quite the opposite and can take it. 

Here, [url=https://en.wikipedia.org/wiki/Chin_(combat_sports)]wikipedia[/url] talks about it. In ordinary people, who don't fight for a living, you might be right. But Arena combat is seldom about ordinary people scrapping, and when it is, it's rarely got one person who can deliver a pin-point knock out blow to the chin against a man who can't.

Fights in the real world are often quick because of a huge skill disparity, or luck. Neither of which should really be a factor in arena fights, which are more like formalised duels in structure.