It isn't weighted any less than the rest. The RNG is "special blend" so to speak. It uses a tactic that raises the drop chance of items you have already received this lower the chance of the ones you haven't. So if you have played since launch you probably have most exotics. Do the few you don't have are very hard to drop. Obviously this extends your grind towards those last few guns. Sadly for some this gun was Gally and it became extremely hard to get. I got one like my second VOG run and have since received 9 of them but it took me until a month ago to get hawkmoon.