Embers Discussion: Spoilers from Ch 30

[Black Aeronaut]

Personally, I don't think it is really character assasination as much as it is more like a real-world portayal. Observe these comments by the Author:

In I Could Do Anything, If I Only Knew What It Was, Barbara Sher describes the rage against the ordinary. Ragers are charismatic, often skilled, often geniuses. They work hard, they may be good at what they do - but they want to be the absolute best. Without having to start from the bottom. Or put up with the ordinary scutwork the rest of us take for granted. They charm people around them into fixing their problems, over and over again. And they always have problems. Because when they were young, they were horribly betrayed by the world - and they want to be rescued. More than anything in the world. Katara's central motivating idea - the Avatar will return - fits the rager's profile point by point. 1) Her fantasy requires the act of an outsider to come true. 2) The end is a rescue or reward that comes only to special people. 3) She'll be "discovered" as special (the last Southern waterbender). 4) Her life is pointless without this happy ending.
This can be fixed. Ragers can learn to find the root of their problems, and move past it. But it takes hard work, self-examination, and admitting a little brat inside you wants something it can never have. Katara can break out of this - if she listens, really listens to her family and friends, and realizes that she wants, desperately, for someone to make things right. To rescue the little girl who lost her mother, and grew up too soon.
Except in canon the creators hooked her up with Aang, who wants to be mothered and have excuses to be irresponsible.
(Insert writer banging own head against wall.)
...Yeah. That relationship is going to end so well. I think I'll take my chances with Azula....

And if you look at the bibliography he has there, you can see that what he is doing is applying real-world rules to each of the character's psychological makeup, background, and culture, and rewriting the story accordingly.
As for the power-ups... chill.  Zuko ain't the only one.  He's just the one that gets the most screentime.  And I strongly suspect that there are others that are going to wind up bending more than one element later on down the line.