I recently saw what you said about Kikyo not doing anything positive for Kagome after realizing Kagome's kindness after she healed her and I agree so much. That went nowhere because it feels like Kagome was the only one doing kind things for Kikyo even though she has little to no reason to feel compelled to help. She could've definitely apologized the way she treated her at the beginning of the series.
Yeah, that’s one of my main beef with Kikyo’s character arc. She does a lot of bad things early on in the series that are just... completely swept under the rug. Kagome’s feelings towards Kikyo are only portrayed as “jealousy” when she has plenty of other valid reasons to dislike Kikyo, that Rumiko never brings up after a certain point. And when she does mention it, like in the Mt. Azusa arc when Kagome mentions that Kikyo used to want Inuyasha dead, all we get is Inuyasha saying “she’s not like that anymore” and Kagome agrees. It feels cheap.
I get that Kagome is the protagonist, so it makes sense that she’s the one being challenged and tested throughout the series. But at some point when Kagome constantly saves Kikyo, always has to “learn to respect Inuyasha and Kikyo’s past” and we don’t get a single scene where Kikyo does the same for Kagome, it feels very unbalanced. Some people will argue that Kikyo is the mature one because she “stopped trying to interfere with inukag and just minded her business” but.... not actively causing harm is just the bare minimum and ignoring the harm that you’ve already caused is not a sign of growth or maturity, in my opinion. It’s also easier for Kikyo to “get over” the negative feelings she initially had for Kagome, when Kagome has been nothing but kind to her from the beginning.
People also sometimes try to argue that Kikyo helped Kagome by giving her an arrow to fight Naraku when they were looking for the last shikon jewel shard, but she only did that because she was weak (after almost getting killed by Naraku on Mt. Hakurei) so she couldn’t go fight Naraku herself. Or people argue that she helped Kagome by giving her the bow from Mt. Azusa... when really all she did was give her the directions to get it, and then she died so she wasn’t going to use the bow anyway.
I don’t even care about Sesshomaru, but I can recognize that he “redeemed” himself better than Kikyo did. He tried to kill Kagome twice at the beginning of the series, but then he directly saved her life twice later on. He constantly tried to fight Inuyasha to steal Tessaiga from him, but at the end he willingly broke Tensaiga to give Inuyasha meido zangetsuha. He’s not a good person at the end of the series, but his wrongdoings are balanced by acts of “good” that directly benefit the main people that he wronged before.
I feel like Rumiko’s mindset towards Kikyo is that, well, Kikyo is the one who objectively suffered the most, she is doomed to a tragic fate while Kagome is the “lucky” one for being alive, and she wasn’t a bad person before being resurrected as a vengeful revenant, so that means she doesn’t need a redemption arc. But I disagree with that mindset because good people can do bad things and still need to redeem themselves for it. Just look at how Sango apologized for stealing Tessaiga from Inuyasha, and how she apologized to Rin for almost killing her (AND risked her own life by giving her poison mask to Rin to make up for it).
Also causing hurt to other people because you’ve been hurt is wrong, even if it’s something we can empathize with. Again, Sango is a good example because she suffered a lot too but she doesn’t use that to excuse her wrongdoings. Or Inuyasha, when he transformed into a full demon and slaughtered a bunch of human bandits, he immediately tried to prevent that from happening again by working on mastering Tessaiga. Kikyo “wasn’t really herself” when she was first revived, but neither was Inuyasha when he transformed, and that didn’t stop him from taking accountability for his actions.
I don’t think Kikyo needed to explicitly say “I’m sorry” to Kagome, but any positive actions towards her would have been welcome. I also feel the same about Koga, but since Koga’s character is not very important to the overall story and he’s mostly treated as comic relief, I’m not as annoyed by it. I’m more bothered by Kikyo because I think she’s extremely interesting as a character and if Rumiko had tried less to make her look good, she would have ended up being a better character.