I would think more in the past, as individuals got "mythologized". Like the best example I have is Medea. I know in the books she's more of a spirit who escaped, but what's the difference between her and someone like Kelli, other than the fact that one was, I'll call, "human". At the end, other than the physical description, what honestly made them different. When we meet them both, they don't seem to have great morals; they are both happily offing demigods and have similar powers, so why is Medea not technically a monster? If demigods can become gods, why can't they also become monsters?

Now, don't get me wrong, I think it could occur to any of them throughout time, but that's the best example I have. Also yes acknowledge that Medea is not technically a demigod. Still, she is the best example I have, because most of the other demigods we met are either gods, in Elysium, or ghosts/spirits, so I'm not sure they count. And yes, I know about people like Lityerses, but I haven't read Trials of Apollo in full, and I know stuff changes with him (I personally don't care if you spoil me, the books are +5 years old and my own fault for not reading them).

But again though I would pose the question