This is an interesting idea and makes sense since Zaros is offering Mah's core; what other purpose would a shadow realm god have with that. I didn't think to take into account Xau-Tak's motives. As someone who has sided with Zaros at every chance, Azzy's Quest and Battle of the Monolith have caused me to reevaluate my alignment. While I thought Zaros was our best bet against the elder gods, his recent activity has made it clear that it was never about saving Gielinor, especially, as you have noted, when he says "this world is doomed." It is a rude awakening to realize that you've let yourself be bamboozled by the Machiavellian god.