How, as a lawyer, do you argue that a punch to the face is a disproportionate response to a punch to the face? Did he wind up and throw a haymaker? Did he double axe handle her in the back of the head? Did he pummel her mercilessly on the ground? Did he put on brass knuckles? Whip out a club or knife? Pull a gun? He responded with proportionate force to an assault on his person and stopped his attacker... after she wrestled herself free of his previous non-violent attempts to stop her assaulting him.
The only way you could argue that he was not justified is if you argued that a grown woman is physically incapable of harming a man with her fists.
I don't believe he, at any point in that confrontation, was in danger of being injured to a degree that would justify the level of force he used on her. She threw a sloppy punch while being restrained that a) mostly missed and b) wouldn't justify the level of force even if it didn't. He can continue to restrain her or simply remove himself from the area.
I can't for one second believe anyone who watches the video believes those two punches were equivalent.