I agree with you 100%. I was just telling my wife this same theory (she plays with me). I really think Bungie randomly assigns each account created with a certain weapon drop percentage package. It's just like you said they have to control the weapon flow of the game and also keep people busy, always searching for that unicorn. For instance she had two Thunderlords before and an icebreaker before I had either. Then on my side I was getting multiple Hawkmoons. Just because something is RNG doesn't mean results can't be weighted.