I could be wrong, especially because I myself did not read it and was told the spoiler, but I think the Jeannette's existence itself was killing Claude, which. Very fucked up and completely unnecessary, imo. I don't know if, in that other universe/whatever she has a familial, loving relationship with Claude or her bio dad, but regardless, convoluted is a freaking understatement.
Instead of going for a route that'll give happy endings to as many characters as possible, I would've had Jeannette realize the nature of her existence and exactly what she is, her dealing with the horror of it and existential crisis up the wazoo, and then, I don't know, possibly ultimately have her sacrifice herself to save her father (never mind that he's not her bio dad, she considers him her father and really, the truth is being kept from her to begin with, so I can see them continue to keep it from her) and deal with the ramifications of that.
Athy could've matured from it, develop a sense of compassion and empathy, and become an advocate. For what, I don't know. Maybe for orphans who crave family the way Jeannette did or something like that. It could've been the reason for her to learn magic instead of the reason that was just presented in this latest chapter, to really refine and study it so that should something like this ever happen in the future, death wouldn't be the only solution. It'd be a good way for her to start getting closer to Lucas and build a relationship with him.
And Claude could've prosecuted his brother through legal means for not only using that dark magic thingy but also attempted regicide and conspiracy (though, tbf, I don't know if he did or didn't or if he just offed him) and Mr. White for conspiracy (keeping and raising the daughter of the king in secret with the intent to possibly manipulate the king through his love for her (which never came to pass) and to marry her off to his own son (so, what, that his bloodline will enter the royal bloodline??)).
Jeannette could've gone out a heroine, a savior, and it would've been terrible and fucked up and sad in so many ways, especially considering that she's a fucking child and shouldn't have had to deal with this to begin with, but I think it would've been better than jumping through hoops and sharks to give everyone a happy ending that's now cheapened.
(I also would've liked to address the fact that Athy and her dad's relationship is built on deception, which is a trope of this genre that I fucking hate, but that's never going to happen, so.)
Sorry for the rambling, I've had a lot of frustrated thoughts about this ever since my sister spoiled me.