Actually, to be clear, Dregoth wanted to give the world to humans. He didn’t develop the Dray until well into his hidden exile.
To be honest, if it weren’t for Borys going kookoo coco puffs at the time of the rebellion and Rajaat’s imprisonment, I think it’s incredibly likely that the champions would have continued the wars and wiping out everyone but humans. But with dealing with Borys, they had to fortify themselves in their cities, making it difficult to continue their cleansing. Over time, faced with the absolute destruction Borys was waging, they probably refocused on more immediate issues. After the dust settled and Borys became sane again, when faced with the reality that Rajaat’s prison would require life-force sacrifices for basically eternity, why not keep those subhumans around for that?
Another thing to consider is that the champions likely have different motivations for joining up. Hamanu, for instance, doesn’t give a flip about anything other than trolls. And he killed them all. After that, he was done, and didn’t care one way or another. Of the remaining surviving champions, only Andropinis, Dregoth, and Borys hadn’t finished their races. Dregoth surely WOULD have continued his wars if he hadn’t been assassinated, but Andropinis and Borys likely stopped caring about wiping out the elves and dwarves because of the change of status quo and their potential uses as prison-fuel. I imagine for a very long time, though, that there weren’t hardly any (if any at all) elves in Balic. As it stands, Elves and Dwarves probably don’t have a very warm welcome in Balic and Ur Draxa.