There's still recognizable traits of Ilya in her Prisma!characterization. Not all of them--the biggest change seems to be the lack of murderous rage, but all I've seen is the anime adaptation so far (which, I'm told, is remarkably accurate to the manga).
As for your hypothetical example, well, as you can see with a LOT of fics, people eat that shit right up! I'm not saying that's good, though, or ideal.
Honestly, though, it just sounds like you're remarkably bitter about the spin-off, which is understandable. But frankly, I don't care. I'd rather see Satsuki get her route than Ilya get hers.