One of the meanings of the word vexed is
to have an internal conflict, so think of the vex they are one mind whose sub divisions have conflicting views (see the worshippers of the black heart and the military divisions) again with bungie cleverly naming things.
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The Vex are operating in the same way that Rasputin is. The war mind is running scenarios to find a way to survive/win the war against the darkness. The Vex are doing the same thing. The only difference is that the Vex put the scenarios into practice for real world testing against their enemies. That's why you see different approaches from the Vex. But they all answer to one mind somewhere in the universe. All fight for the same end goal.