Fair explanation, and thanks for taking the time to do so. My point though, is that not only could someone of Asian decent look like him, but people from other ethnic backgrounds can as well. The apparent cultural setting, really shouldnt matter. For example, there are light skinned people who have a steriotypically dark skinned culture, and dark skinned people with the reverse. Like many white people in Africa, or blacks in the Netherlands, Germany, the UK, etc. Race is not a black and white subject, in fact there is frequently more genetic diversity in an "racial" group than between different groups. Which is why racial categorizing is misleading and problematic.
Zuko is a cartoon character, and he will never look exactly like a real person. All we can do is patch something together based on his skin color, hair, bone structure, eyes, etc. There will always be a bit of imagination involved which is why I think a lot of people like to side with whatever is most comfortable to themselves. Some people see Asian clothes or hairstyle and immediately assume the character must be Asian. That may make sense to them, but with a greater depth of knowledge or world experience those people would know that that is an ignorant view point. If you have read anything in history about persons from different cultures meeting, it is really easy to see how hindering those types of thoughts can be.
Zuko is from the Firenation, and has no relation to the real world. Therefore there are no limiting cultural or "racial" standards set in place by the creators. Furthermore, because "race" does not exist as a functioning scientific term, it is impossible to try and use it in a way to appropriately categorize someone. All we can say regarding Zuko is, "this person looks like him" or "this person doesn't." Which is all that should matter anyways. Why try to limit anything when it is not necessary or even beneficial?
Perhaps you want to promote someone most similar to yourself, in an attempt to enhance the quality of your own life or your chances at reproduction, but as I said before there is more genetic variance in a given "race" than there is between them. Plus just because two people look Asian does not mean they come from even remotely the same background or culture--a subjective term in itself. It is completely irrational and often times one of the biggest problems with the human race.
By the way, I'm not trying to offend or argue with anyone here. I just wanted to explain why I feel limiting Zuko racially is counterproductive. If anyone is interested or offended by what I had to say pm me instead of posting here, so we dont start any arguments.