Suggested by Eric Zuko and Ozai are both powerful fire benders. While Zuko always seemed like the big rival of the series who would go on to be the very best, it seems like he never quite surpassed Ozai. That, or he never got to show off any abilities that would put him above the older bender. Ozai’s physical abilities are just as impressive as his fire and that allows him to dodge very fast attacks and endure others. Zuko just doesn’t have that same level of physical ability to support his elemental abilities. Ozai wins.