I tried to make an argument about why Kaija didn't deserve the hate, then I saw that her route is different based on your/MC's response to certain questions so their past (predating the events of this game) is fluid and not set, which I don't think was the best way to go about that. It makes her not her own 'person'.
My first run was with Kaija, but then I tried the opposite route and I was confused to all hell about her emotional 180. Kate is best girl, but Kaija is far from worst girl. Medb is worst, by far, and I hope I get to kill her like I killed that blonde bitch who challenges the MC to a fight to the death. Their reaction to how that ended tells me all I need to know about them. The Elves are hypocrites and should be eradicated. I'm siding with the ImperialsTemplars on this one.
Eh Honestly can't really understand the hate Kaija gets, even if you don't simp as long as you respond with a certain level of calm and keep it respectful she doesn't really come off as that bad, i feel like you have to go out off your way to provoke a negative response from her in my experience. And while it is true that making her emotions and stuff work around the MC makes her lack as an individual character it also means that you literally can't get that response unless you actively push for it, The MC is rightfully mad about being lied to and being cold to her makes a level of sense but even if you make it clear that the relationship is over and all, unless you are an intentional dick she doesn't respond negatively.
And form a characterization perspective it really doesn't make sense for the MC to be a downright asshole to her and give her grief on anything except it's specific to the relationship, she goes out of her way despite her orders to rush back and save you on a gut feeling and if you have been decent to her up to that point she clearly shows she cares about the protagonist, doesn't mean you have to act like she didn't betray trust but she is clearly not doing it out of ill will and regrets the choice unless you have been intentionally negative to her at which point it would make sense for her to see the MC as a job rather than actual relationship.
Medb is not all that bad either after you get through the wall she doesn't come of as a bad person, concerning the duel a negative response for killing Finnabair makes perfect sense imo, you can't really come with the intentions of preventing a war then kill someone on your first opportunity even if they did have it coming and expect people to accept your plea for peace when you do otherwise, it's not really a hypocritical thing in my opinion that's just a valid response to the actions the MC takes if you go that route. Especially when you consider the fact that the only reason you even got the opportunity to even argue your case at all was because her father was polite enough to bring you to argue your case when he would have had no issue killing you immediately.
If you don't kill her, from a logical standpoint your plea for peace looks more genuine to them and from an emotional standpoint you avoid killing an elf right in front of her people and sowing even more negativity. In fact if you don't kill her, every action with the Alfar from that point forward is positive, with a bit of passive aggressive banter with Finnabair that leads to an eventual friendship with her, and Medb outright states that she honestly didn't believe in a possibility for a somewhat peaceful resolution but your actions convinced her otherwise so your actions there are a major factor in the decision. Hell if you show mercy after an unfortunate circumstance the king trains you for a bit and states that he was interested in getting a feel for you himself.
You can't choose to take antagonistic, provoking or an aggressive stance and expect the characters in story to respond passively or positively, if nothing else I think the fact that scenes play out very differently depending on character choice makes the game significantly better since actions do actually have consequences. Believe me I wanted to off Finnabair as well because of how overly aggressive she was but I let her go because it was counterproductive to the MC's intentions and i ended up liking the Elves you do speak to afterward, hell by the end I grew to like Finnabair despite how she started and I was kinda annoyed by how the chapter ended since there was some level of character growth that got wasted.
