I think a lot of people forget that Zuko was NEVER the villain. Like yes, he was an antagonist, and a foil to the gaang, but he was never a villain. Even back in season one, Zhao was the villain not Zuko. Then Azula and eventually Ozai in seasons two and three respectively. We are meant to root for Zuko from the beginning. He is always cast in a sympathetic light, even before we learn his backstory.

That’s why his redemption arch works. From the beginning he was framed against and outside the Fire Nation. In literally the third episode Zuko is pitted against Zhao and is shown to be more honorable, merciful, and different.

Zuko was never a villain, he was just misguided and an abused child who wanted his father’s love and acceptance.