Other cards indicate the Vex to be older and found on worlds colonized by humans and to be almost time imortal. For your theory to be right Rasz would have to have gone back in time to create a force to fight the darkness in the form of the Vex and than seeded it throughout the unverse. But multiple sources all claim the Vex is eviler than other evil (Cabal Fallen Hive) and those are all supported and aiontied by the Darkness to be more powerful (like guardians) I don't know if fans would accept a story conclusion like that in the form of a AI decided that the only way to save humans is to kill them after the fiasco of the Mass Effect ending. Odds are though we won't know and even if the rumors of their original vision are true I doubt the answers to these questions were to be raised in the first game.