Sorry, but having Zuko actually fight back against Ozai during their Agni Kai is just wrong. He was a child, only 13 at the time, afraid to fight his own father and was mutilated as punishment, because Ozai saw Zuko's begging and unwillingness to fight as unforgiveable weakness.
The Angi Kai isn't meant to be a showcase of Zuko's fighting potential (that's what the Zhao fight is for), but to show the utter cruelty of Ozai.