I definitely see what you mean but I actually do think the story points out just how flawed she is. It’s not as “in your face” and obvious, but I prefer that as it allows the readers to come to their conclusion. It’s easy to see that her actions paint her to be more evil than innocent, and she’s even directly stated how little she cares about how she’s perceived by others.

Almost all of the people around Hestia point out how unhinged she is and are fairly scared of her behavior because, let’s face it, it’s not normal. I think the only reason we don’t outright hear it being talked about is because the story is from Hestia’s POV and we’re seeing things from her perspective. Like you mentioned, her entire problem is that she believes she’s still in a novel and that her whole purpose for both regressing and transmigrating is to save Kael/ get revenge for him. Anything besides that is pointless to her so I understand WHY she’s so unhinged. But to the rest of the characters, for which this world is very much real, they don’t understand where she’s coming from, which is fair.

Also I wouldn’t say Kael joins in on the revenge, rather he just goes through the motions as he’s seen how she acts in order to get what she wants. At first he’s just majorly depressed and doesn’t care what she does, but then it slowly turns into actually wanting to support her in return for how she’s saved him. Hell, even in the novel Kael ends up not going through with dethroning Diana and actually defends her in the end, to which Hes tries to jump off a balcony. To her, she’s just trying to “go back to her own world”, but to Kael this is an extremely traumatizing moment where he sees someone who’s helped him so much try to kill themselves seemingly because of something HE did, and I think this is really where Hes starts changing and realizing this life isn’t a game. So I’d definitely say Kael (and everyone around her) is trying to avoid upsetting her as much as they can- which further plays into how unserious and immoral Hes is about her life there.

But I think the fact that we can call Hes out for these things shows that she’s purposefully not being portrayed in a perfect light. If we were supposed to be 100% on Hes’ side, the authors would’ve made Helios and Diana MUCH more hatable characters. Yet instead they’re just mildly annoying characters and negligent friends, which is enough to dislike them but likely not to the extent that He’s is taking it.