I just had a thought. One of the oldest questions with this setting is “Why did Rajaat bother with champions? He was practically omnipotent, why not just do it all by himself?” and one of the oldest answers to that is “Because he’s insane.”
Ignoring (for the moment) everything else, what if he weren’t “just” insane? What if there was rhyme and reason to what he was doing?
I suddenly remembered a graphic novel I read years and years ago called The Life Eaters by David Brin. Basically, during WW2, the nazis were systematically gassing people not just for the lulz or because they were crazy. It was all part of a necromantic ritual. All of the millions of people that they sacrificed, the life energy was collected and used to give “birth” to the Nordic pantheon of gods. And with a real-life Thor and Odin and all the rest on their side, the Nazis essentially conquer the world in short order (until other countries start discovering the secrets of this magic and start putting it to use, sacrificing millions and millions of their own citizens to make their own “gods”).
So we know when Rajaat escaped in the Prism Pentad he was basically turning the champions into mulch, practically unopposed. That’s a lot of power. It seemed like he was all set to do everything himself this time (with some lackeys like Tithian thrown in: remember he explicitly said he was going to grant Tithian’s wish and make him a champion). Even the sun turned blue again.
So my thought: what if, through some complicated scheme involving the nature of the champions’ power, and maybe the empowerment of their armies (like templars?), the cleansing wars were acting like one big, millennia-long sacrificial offering? And all the life energy from all the races and individuals being killed was being collected in a centralized place/item, all for the use (by Rajaat) to either remake reality into a facsimile of the Blue Age, or literally travel back in time and rewrite reality BACK THEN?
You have the unnatural Gray, which could be connected to this. Souls do not leave Athas, they get stuck in the Gray. This is canon, and—per other TSR-era materials—completely unnatural. You also have the Dark Lens, which wound up being the key to Rajaat’s escape from the Hollow (and ultimate defeat), and could be a repository/tool to access all that stored power.
If I recall correctly, in the Ashes of Athas adventure path, one of the possibilities was Dregoth literally sacrificing the ENTIRE race of Dray to—I think, this part is fuzzy—permanently seal Rajaat’s prison, making the dragon levies unnecessary. That’s precedence for something like this.