We can fucking see this in the day of black sun episode too. Zuko does not tell Ozai that burning half his face off was cruel and wrong. That's not what he says. He tells Ozai that dueling with a child and banishing him for talking out of turn is cruel and wrong, he never directly addresses the scar and jumps immediately into the politics of his decision. He does not think Ozai burning off half his face was the abnormal part of that situation. Or at least, he doesn't think it's abnormal enough to warrant mentioning, and the agni kai and the banishment are things that are specifically within Ozai's power, that are directly identifiable as things Ozai can uniquely do.
And that's not the only episode we see this in, either. All the way back in the storm, when Zuko's crew learns how he got his scar they're not all "oh wow our firelord is such an asshole for burning off half his child's face" they're "okay well it was a little fucked up for Ozai to challenge the kid to a duel but the rules are the rules, it was the firelord's war room and it was the firelord whom zuko disrespected. the banishment's totally normal btw." and they go about their merry day. Zuko has zero cultural frame of reference for the way he was treated being abnormal, and even if you want to say that the dozens of people who witnessed Zuko getting burned and did nothing (even Iroh! All he did was look away, Iroh couldn't even get it through his head that that shit's not normal in the moment, we can watch him go through his arc the more he travels with Zuko and I do believe it is watching how badly Ozai fucked this kid up that gets Iroh to chill the fuck out with the war crimes) as just the upper echelons of society, if how Aang was treated by the headmaster during the parent teacher conference in the headband is any indication, that kind of behavior is likely normalized in the common fire nation culture, at least somewhat.
And we all saw the boiling rock, we all saw Zuko take 10000% of the back seat to Sokka's leadership and yeah, showing Sokka how he handles a teamwork situation and taking directions from others is how Zuko wins Sokka over, but that's not a conscious decision on Zuko's part. That is Zuko responding to Sokka going "hey I fucked up with this war strategy thing and now I've been dishonored and need to do this impossible task for my father to regain my honor" by saying "yep okay I have the experience in this exact situation I can help you avoid the pitfalls I ran into (example: the north pole) and I have insider information on the exact prison you need to break into and out of, yes I am helping you with this now, no I don't know why I'll be dissociating the entire blimp ride home"
But he is, notably, getting there.
Like I've talked before about how everyone's field trips with Zuko fit with what they need to see from him in order to trust him, but everyone's field trips with Zuko also parallel his own journey up to this point and in my opinion propel him to work to that point where he fully realizes that what happened to him was not normal. Because while he's definitely not there at the end of the series (see above), he does directly call Ozai a terrible father (not just a monster hellbent on destroying the world) in the finale, after Katara finds the painting of baby Ozai.
Because like, okay Zuko and Aang's field trip mirrors not just Zuko's early struggles with firebending but also the heavily implied period after Ozai burned him where he could not firebend as well as he used to (he was running basic drills at the beginning of the series when in nine months max he'd be the fucking avatar's firebending teacher). Zuko and Sokka's field trip, as stated earlier, mirrors his quest to regain his honor. And Zuko and Katara's field trip mirrors confronting Ozai. I don't think the Yon Ra to Ozai through-line at the end is a coincidence, and I don't think it's a coincidence that Zuko asks Katara to go with him to help him take down Azula. I think watching Katara confront this person who's hurt her so, so badly while being a person who hurt Katara so, so badly but then he, Zuko of the Fire Nation, gets forgiven by Katara? What??? He never went into that expecting forgiveness he just didn't want Katara to hate him anymore, probably because Not Being Well Liked has historically led to Terrible Things Happening to Him and he's been on a role lately with this whole "building interpersonal relationships with the gaang" thing. And that's not to diminish Aang and Sokka and Toph's forgiveness, but Katara was right when she said she was the first one to trust Zuko and she was the one he betrayed first in Ba Sing Se. So like, that forgiveness is not little to Zuko, especially after everything he's just seen.
Like I know we all like to joke about Zuko being scared shitless seeing Katara bloodbend a dude, but I think that moment of "oh, she could have really hurt me, and chose not to, because even after all that she did not think I deserved to get hurt like that" combined with both like... like he didn't get a lot of time to observe Hakoda Katara and Sokka's dynamic but I think what time he did get as well as Katara telling Zuko about how she and Hakoda fucking ran to Kya to try and save her in time gave Zuko a much needed nudge in the right direction. Like again he's still not fully there yet, but on some level he knows that Ozai wouldn't have done that for any of them, if he were in that situation, and now he knows, on some level, that what happened to him goes beyond Ozai just being an evil dictator.
And I think it takes Zuko a very very long time after the war to get to the point where he can talk about it at all.
