I can't really see Kirk first calmly arranging for Mitchell's ultimate destruction via radiation bombardment, and then succumbing to red haze and deciding that he absolutely needed to punch him in the jaw as well...
I don't mind punching Gary to further make him dazed and confused, but if you're going to kill a guy, a punch to the gut, a double fist to the neck, two chops and a flip aren't the best ways to do it. A punch to keel him over and then choke the life out of him. Or grab that rock a little sooner and don't pause to ask for forgiveness.
I love the episode and the fight is great, but it just seems a little silly that the intent to kill is depicted in a standard TV style brawl. Of course, with the clarity of 45 years of watching the episode, it's easy for me to say stuff like "I would have bought it if Kirk tried to start with a killing blow, but Gary blocked and it became a fight as Mitchell defended himself." The episode was still awesome from start to finish and sold the series. I'm nitpickin', but only to pass the time.