I've read a criticism of how TOH handles redemption arcs, and I can't help but agree with at least some of the points.
Basically, the way TOH handles redemption arcs is overly simplistic-a character starts out antagonistic, but it turns out they were really manipulated by a cardboard cutout villain and actually a sweet person all along. It seems a character is only "worthy" of sympathy if they were never bad in the first place. It's a concept that could work, but feels lazy when applied to several different characters.
When we look at the major redeemed villains Lilith, Amity and Hunter, they all follow this pattern. Lilith is introduced as strict and austere with an intimidating presence and dresses in all black, Amity is aloof, haughty and a bully and Hunter is cocky, but after being redeemed and joining the good guy's side they drop these characteristics and are revealed to have a nerdy side, becoming more similar to Luz.
Lilith becomes the Cool Aunt, Amity becomes Luz' caring girlfriend and Hunter becomes the "resident whump character". This would be like if Zuko lost his fiery temper and sullenness and become a cheerful goofball just like Aang.
While I understand a point being made that once these characters are freed from their toxic influence (2/3 are Belos, and the other is Odalia) they gain the freedom to embrace themselves, so the changes post-redemption provide a stark contrast to their antagonistic selves, but I still think it sucks that characters like Lilith and Amity lost their unique personality traits in favor of becoming broadly "nice".
Another point from the critique I'm referring to is that with the exception of Lilith, none of the former antagonists go through a "redemption arc" because they don't make up for their previous actions. I don't know if I agree with this broadly, but as for Amity I think it might have a point; she didn't properly atone for bullying Willow, and she did it out of her own free will because Odalia had only demanded she ended their friendship, not any bullying.
"Nice" isn't synonymous with good and I would love to see that represented in media.
Thanks for your ask. This is something I've pondered quite a bit. There are many reasons why I personally disagree with a lot of this.
1. For lilith, she never really does become that nice after her redemption. She spends most of Echos of the Past unamused at the others' hijinks, trying to prove herself right and being harsh towards luz and King. In yesterday's lie, she crushes King's hope of his father coming back. She's still harsh in her personality.
2. For hunter, I don't really think he loses his cokyness, it's just either ignored or not recognised by most viewers. Like how in thanks to them he brags about his pain tolerance (before being hurt and wincing before he can finish his sentence) confidentiality showing off his cosplay. (And although it's before his true redemption, any sport in a storm is always pointed out as an episode where he's acting out if character, but in that episode he's about the cokyiest he ever is, imposing his point of veiw as truth and assuming he knows what's best for the emerald entrails before he tries to make things right)
3. For amity, I do think she did change the most in personality (although she still has moments of harshness, like judging hunterfor his costume choices), which I don't see as that much of an issue given the others don't do that as much as people seem to think and because when she is like that, she seems miserable. She spends most of her time disconnected from everyone around her. She's lonely, and as a result, she doesn't really care about how nice she is, and she's rewarded by her peers (and probably parents too) for being mean so that's what she does. For her, I feel like becoming more nice is a result of her having real friends, and because of that, learning to be mindful of others and becoming more like them.
4. I feel like a lot of them definitely at least try to make up for their actions, especially lilith, who shares the curse with Eda, making the curse more manageable for Eda and making Lilith's actions have consequences