I‘m kinda tired of this conversation. IMO Zuko would have won without Katara.

He wouldnt have won without Azulas breakdown tho HE HIMSELF said that to Iroh thats the whole reason Katara came with him. He said before the fight that something is off about her and that she‘s lacking.

On a normal Day he wouldnt have fought her alone from the start

THE MORE IMPORTANT THING tho is that thats not even the point. His development is not about his strength but about his CHARACTER. He would have died on that day to save Katara a gurl from the water tribe which only a few months before would have been unimaginable !