By the way what's the Scorpio's magic then? She stole the Leo's one from the tomb but she ...

the "they" might just be a mistranslation.

I also have 3 guesses as to what Scorpio's powers could be. Either it's copying magic, manipulation of objects, or immortality.
The first is self explanatory. With the 2nd I'm thinking since she's been around for so long she must have shared her magic similarly to how she's doing it rn with the manipulation magic - so she could basically be the foundation/ancestor of modern day magic. And the third one might just come with superior constellation mage territory or they actually lived mortal lives with Scorpio as an exception, hence why she's still around.
It's something that must have been weak in comparison to something like mental and nullifiction magic surely, at least that would explain why she wants it so bad.

Ah I forgot about the translation haha.

By the way your guesses are valid. Cause if I were to take the she's immortal then it really explains everything cause it's true while the others had power but were mortals she had her power of immortality. Though the the first guess I'm not sure about cause then she wouldn't have had to steal the manipulation magic from the first emperor's grave or so. But I agree with the rest though she might have around for so long so of course she's learned all the knowledge about other magics which the others had, and even coming in possession of them is not impose for her.
Oh and another thing came to my mind as I read your explanation that Pelles' magic she wants and as you said it might be true that the one she stole maybe rather weak cause that would explain that Win was somehow able to nullify the effects even if for some time, and that maybe he needs to manifest it to the most of his ability to use the true power his bloodline holds, not unknowingly as he did but with free will or might as that he's the reincarnation of emperor Julian/Julias. Though she has some ability to maintain it for a longer time maybe she harnessed her powers or maybe she uses bloods or other mediums as we saw already that she took it from Binka.

What I mean is that Scorpio's original powers must've been weak. That would explain her thirst for the mind magic, babygirl has an inferiority complex.
But yea the powers she stole are no doubt a bit weaker than the potential that Win possesses, since the blood she uses is from people who didn't do the inheritance ceremony. Now that I'm typing her powers might also be blood magic, but anyway-

I think the ceremony is also why I wouldn't go out of my way and agree that Win is a reincarnation of his ancestors. He is a talented mage, and perhaps there is something about the ceremomy (+his bloodline as you said ofc) that unlocks his mind manipulation skill tree to its fullest potential.
What's for sure is that there's something about what the first Emperor did by ascending as this quasi guardian deity. I think most of our conclusions will be proven wrong or right depending on whatever it is he really wanted to hide away.

You might me right about that, her having blood magic. Oh and that was actually just my speculation that Win could be the reincarnation or rather the most promising potential for the mind manipulative magic to appear after the first emperor (?) His father didn't really show anything of that kind or told him anything because regarding their relationship he would have known something about how to control it. It seems the magic is most powerful in him in all generations (after the first of course).

Oh and yes all these speculations of our might just be proven wrong, maybe it would be very simple something or their might be some plot twist.