1) If you think dragons are evil and should be eradicated, Apex offers you exactly than only minus all the unnecessary destruction at the cost of some delay. And I can't for the life of me think of any reason why you'd trust her less than a mad scientist who repeatedly tried to murder you.
Yeah, assuming APEX tells you the truth... Pretty big if there. And you know it's unreliable, and of course you may be turned off by the fact that it destroys peoples brains for fun and profit, lik evidenced by the cult.
Listen, I get that siding with APEX made sense to you or something. But don't pretend that there weren't some very good counterarguments. But this is an irrelevant aside anyways, because
even if siding with APEX is an option, destroying the dragons will be hard, and supporting Vauclair
and allying with APEX makes perfect sense if your goal is killing dragons. "You can side with APEX"
isn't a counterargument at all.
2) If you want to side Vauclair - why on Earth do you think that he'd like to side with you? He has absolutely zero incentive not to just kill you, whatever you think of his motives and actions.
You just rooflestomped all his minions, you could just turn tail and leave him to his plans. You know he's gonna execute the plan, he has just spent fifty years and all his life planning it after all.