Yes its random in the vault but you can only get it in the vault any mmo will have a random factor that is how the games work. If all you had to do was run through the game and then you get to choose a piece of armor everyone would be level 30 and it wouldn't be as hard or as much as a achievement as it is.
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The final boss should never give trash like a shader or a ship or three shards. A sparrow? Fine. At least it's something you can use. You should never get a class item that can't even be broken down into shards from a chest that other players are getting exotics from. At the very least these class items should break down into more shards than a normal piece of armor. Cosmetic/useless items/ascendants are not adequate boss drops.