I got the Vex from the exotic chest! It seems there is a another way to get it now! Suck it Elitists! To obtain it you must not get the Spirit Bloom chest! I urge you to bow to me as your leader it also has 336 damage other than the Atheon version.
[spoiler]Did you seriously buy it...[/spoiler]
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Psh. I got mine from the first chest right after you open the vault.