No... It wasn't. The vex of the progeny found the garden, and by extension found the black heart. It's overwhelming power left them with only one action they could process. To worship it. By worshiping the black heart; the vex in this timeline would become transcendent like they have in so many others (there is no other version of the black heart in any other dimension or timeline founded by the vex. That's what makes it so precious.) However atheon didn't approve of this. So he fabricated the vault. (And in another timeline, the vault fabricated him). The vault is a tie between all dimensions and timelines the vex have touched. (And because of this, there is more than one atheon/vault). In the vault, atheon went through many experiments to attempt to bring the vex's paracausal and ontological power outside a controlled environment. (This would mean all the power the oracles, templar, and atheon have inside the vault-erasing things from ever existing- would occur in our dimension/timeline and many others). The vault is no prison for the vex. It is a way to augment their abilities of altering realities simply by thinking. And is another one of the dimensions they completely control The reason we (along with Osiris, and kabr's fire team before us) wanted to stop was due to the fact that if atheon were to obtain the information needed, the vex could use their ontological abilities at max power outside the vault. This would mean all they see imperfect would no longer exist and never exist in the first place. Luckily however; with kabr becoming the aegis (something unable to be erased), praedyth becoming an anomaly, and our/the fallen's/ cabal meddling; we have avoided this outcome in our timeline... For now