I see Zuko always heralded as the archetypal Perfect Redemption Arc in tumblr media analysis and while I can agree with that sentiment, it's important to realize his trajectory was actually very specific.
Because Zuko started as a good person, before he got the scar.
And Zuko has an extremely stable platform of support for most of the show.
Zuko couldn't have done it without Iroh's unflinching, unwavering belief that he could become a good person again. I've rarely seen any criticism of Iroh aimed at his unconditional support of Zuko- for good reason. It's a selfless act.
Similarly, I've rarely seen any criticism of Zuko saying that he didn't deserve Iroh's support. Maybe a few comments here and there about how ungrateful he is at times, or how he should have "suffered more"(?), but never anything outright saying that Zuko should stay exactly where he is in his misery because he doesn't deserve Iroh's helping hand out of it. And this is for a very specific reason- because A:TLA goes out of it's way to show very early on that Zuko was a good person and can be so again.
So Zuko's arc isn't really even a straight redemption arc. It's a recovery arc wearing a large redemption trenchcoat.
This is an important distinction because a raw, straight redemption arc is often unpalatable to the audience, because it starts with someone who isn't a good person receiving a helping hand out of their misery anyway. A redemption arc starts by looking like someone is forgiving an abuser. It starts by having sympathy for the bad people. It starts by engaging with them and listening to them and empathizing with their struggles.
"But they're a bad person, they don't deserve that kindness!" that's the point.
Certainly not to say that it's the job of the victim to be that understanding, helping hand- of course not. And extending kindness does not mean abandoning moral principles and not holding the person accountable for their actions, a la certain flavors of Harley Quinn-Joker romance nonsense.
But someone has to treat the bad person like they're a person if the bad person is ever going to stand a chance of getting better. Regardless of what the bad person "deserves". The bad person has to accept that help, of course, but there needs to be help (and more importantly, kindness) offered in the first place.
(Oh, and. . . this applies to real people just as much as it does fictional characters.)