My experiences in D1 with 3oC have taught me that they usually drop one exotic every seven or so coins that you use. This drop rate is also tempered by the amount of hours you put into the game. The more hours you play, the less you get. For example: I would play four or five hours a night religiously, but see very few exotic weapons, compared to the number of hours invested. A friend of mine who only played two nights a week, about six hours total, would literally have exotic drop after exotic drop. when averaged over the course of a week, we would both have about the same number of exotic weapons. The only difference was time invested. This same mechanic is in Destiny 2. I switched roles with my friend, he became the regular, whilst I became the casual, thanks to the crappy game, and it was I that was getting exotic drop, after exotic drop. I even got to 305 before he managed, despite only putting in the fraction of the time. The game will also give you the drop that you need, if you only play a few hours a week. I have had a suspicion that this was the case in D1, and I believe that it is the case in D2.