actually, your close but not quite there, see since the vex can control space and time, they did simulate the future but only to create Atheon and have him create Time it's self, in a way I'm saying Atheon and Time created each other, yes it's confusing and there may be many flaws in this theory, but the vex can time travel, it's also how they teleport from one place to another, they bend time and space within a small amount of space and bend time so they are sent to the exact spot they want to be, it's a faster way of transportation. and only ones with great power created by the vex can have the power to travel back in time to create it's self and time but first the technology has to be created, and in this case it's the vex. my guess is that sometime near when IF Oryx destroys the vex, they created a vex that had enough power that could know what would happen, in this case a giant super computer killing machine. And it created Atheon and the Gorgons and the Templar and more enemies like them in case Atheon fails at his mission, The reason I say that is because just look at him and the Gorgons, they look different than normal vex, and the Gorgons kill in one hit no matter what; That's a huge upgrade on vex technology, which means they were created in the future and sent back to the past with one mission: "Kill everything that opposses the vex"