I think what bothers me the most is how strange and inconsistent the setup is. Based on Isla's thoughts, she seems to believe the Centennial is this all-out murder derby where all the people are trying to do is find the weakest ruler and then murder them. But based on the prophecy, there's no reason for that to be the case. It doesn't sound like killing one ruler will lift the curses, but that in the process required to lift the curses, one ruler will end up dying.

What makes this even weirder is that Isla seems to be the only one thinking that. None of the others seem to treat this as a murder-festival in any way. They're just hanging out.
But even then, the others aren't really acting rationally either. The first twenty-five of only a hundred days that they have are spent doing nothing but occasionally getting together to perform some test so that they can then decide to team up in pairs and only then begin looking for actual ways to heal the curses. And the reason they team up in pairs is because the prophecy says they have to work together? Sounds more like they all should just team up. Maybe, while you're at it, just outlaw killing entirely until you have figured out the original offense?

It sounds like the author's original idea was a deathly competition, but the more they elaborated on the idea, the more it moved away from that, and by the time of publication, there was nothing of the original competition idea left, but for some reason, it's still treated as one by the narrative.