Well, it's probably more because I'm bad at explaining things. Especially probability. I'm sure it can be calculated much more exactly than I have. Your point is still somewhat valid as the odds of getting any item repeated several times in a row is still small but it could just be bad luck or uneven odds. It could also be Bungie picking everything manually but it doesn't seem to make sense to me why they'd repeat items so much as it annoys everyone. They could be trying to stretch out the grind for Exotic items but I doubt it.