I’m with you until your last two sentence fragments.
Self defense excuses reasonable force. Reasonable force is certainly that which is merely reciprocal, equal. Did the dude shout for help? Did the dude warn him to get back or else? Did the dude have more room to retreat?
It’s one thing if you’ve said “get back or I’ll fucking kill you,” and dude keeps coming; there, the inference of intent to cause serious harm is reasonable. It’s one thing if your backed into a corner and winded.
It’s another thing to be annoyed and not in the mood for bullshit at the food court, so you try to kill an idiot. And it’s a thing called culpable homicide.