Sun Disk of Nerimazeth Theory

Probably nobody in rito even thought about it (im probably the only freak out there even thinking about shurima at this point, this region has been dead since 2015), but: we know that there's a sundisc prototype in Nerimazeth, right? and Xerath is chasing Sivir, aye? Soo, to me, it seams kinda dumb that Sivir was dying in the sand RiGhT In FrONt oF HIM when he was escaping the Tomb of Emperors and he just passed next to her even tho he could literally sense her presence in Vekaura about 1000km away later on. Also, he is soo dead set on getting her ass even tho almost everyone in Shurima seams to know her and hates her and is unlikely to follow her, what couldn't have escaped his attention, since we were told that Xerath tries to learn how the world has changed and its current state. Azir isn't even a killable option rn bc he sure as hell won't quit the capital bc he is told to not be really usefull against Xerath in open desert and Xerath, confirmed, cant win in the capital (and i dont really understand why he wants to kill HIM but not Nasus in the first place).

My point is - Xerath wanting Sivir's ass makes no sense (he literally spared Nasus, the guy who burried him alive, and ya want me to believe he want's to hunt some royal kid, which he has never EVER seen in his life, down because... uhh... because what?? F^^k Azir?).

Soo, I have proposition for a plot-twist that would make more sense than "evil overlord who has no buisness being evil overlord in the first place wants to kill royal bloodline out of pure spite": what if Xerath wanted to activate nerimazethan sundisc,but , only one can be active at the time? What if till current royal bloodline exists, sundisc in the capital is fully controlled by Azir and his descendants, can't be deactivated in any other way than by getting rid of current royality and only after one bloodline is ereased, next sundisc-keepers bloodline can be established and Xerath wants to be independent owner of Shurimian sundiscs?

I had an idea also that he would want to get sivirs blood and 2nd sundisc could be activated at the same time while the other one is active, but after Xerath realised he wont be able to find her, he just blew up the city in hope that she will die somewhere under the ruins, soo that wouldn't make sense.