Six times? You have barely scratched the surface. I just hit my 22nd completion (I have helped out on many phases more than that, just for the experience with no loot) and that is barely a scratch compared to others.
The VoG is not a vending machine, it is designed for people who enjoy that style of play. Some loot seekers are lucky and get a full suit in one Raid, or even two - but few stick with it long enough to get a good plethora of gear.
Try to play with enjoyable people and focus on having a good time in the Raid, the gear will come while you are having a great time.
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The game should still reward you with experience or at the least not provide you with duplicate or worthless items
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The experience of going in there with enjoyable people, is a reward in itself. I do agree, duplicate items can be frustrating (I have one friend who has 8 Praedyth's Revenge, 8!?!?!) - but if you are running more than one of the same class they can be a boon. It is all dependent on perspective and play style. Try to focus on the fun, the loot being random (Which helps it maintain rarity and value), it will just make it frustrating expecting something particular.