
Ah, are you talking about reincarnation or regression? Because time goes back in regression stories. In reincarnation stories, the MC becomes someone else.
I must say that I don't recall any regression story, where the revenge targets looked redeemable and didn't get a redemption arc. I feel like the successful revenges are in situations where the regression wasn't too far in the past and the revenge targets already had their plans in motion or their characters were already developed and were (openly or secretly) assholes to MC.

I never considered this before. Though that's probably because I've never seen a case where this happens. I think we gotta remember that this is fiction. So, while realistically, people in the past may be substantially different than they are in the present or future, in manhwas/mangas once an evil villain is deemed bad, they'll pretty much be that way no matter what point in time you see them(unless they're babies ofc). This is to probably prevent readers from feeling the same way you did. If the abuser/killer is always a bad person no matter when or where, then we naturally wouldn't feel bad for whatever punishment the MC dishes out to them. I can't say this for all manhwas/mangas though since I do see some actually be more dynamic with their side/supporting characters(like showing the readers how different factors in their lives caused their screwed up personalities) which makes the characters actually seem redeemable. But in those cases, usually the MC doesn't seek revenge anyways, or at least doesn't follow throught with it all the way, and instead gives them a second chance or tries to change their awful character. So, to sum up this long spiel of mine, I feel that evil flat characters will be evil no matter what for the sake of the plot, revenge, and readers, but dynamic evil characters have more of a chance of evading the outcome of the MC's revenge by garnering understanding from the MC and readers, going through some character development, and redeeming themselves. Sorry for the long reply and for any grammar errors(im not gonna reread this long garbage to check). Hope no one actually reads this. Good day~~
In mangas involving reincarnation, the girl usually takes revenge on those involved in her past death. But I was overthinking the morality of doing this.
Like when you're reincarnated, time literally goes
back which means the people who caused your aren't in the same headspace as they were in when killing you. This is not to say they don't have those underlying tendencies. But literally everyone has such tendencies and under the correct circumstances, they do come out in everyone.
Obviously if she let's the situation go as it is, then she will end up dying again so she has to change something. I also understand that dying once creates the psychological need to seek revenge.
But I can't help but think if I was in their place, I would feel too guilty doing it. Because once you're reincarnated, are you interacting with the same people anymore? This specifically holds for situations when mc takes revenge on her siblings so when she's reincarnated, the siblings are literally little children and nothing makes sense to take revenge on kids. What do y'all think?