I don’t think the vex are Rasputin defenses, but if a go with this teory then maybe the Vex where created by Rasputin to kill humans and transform planets to kill in mass so the light generated would hurt the Darkness, but this method could be too extreme so the traveler stop the vex (the part where it is said that the vex where stopped by the traveler) And now the Vex trapped in the black barged found a new god (the grimoire card where it is said that they could found in religion a better tactic/algoritm) and that god is now the darkness