I think you may well be correct, that the RNG system is set up to ensure players keep grinding, by keeping the carrot (some of the best and/or most coveted weapons) dangling in front of us for as long as possible. I doubt, however, that certain players are permitted certain weapons and denied others. I think it is more likely that Bungie has set up an RNG system where the odds of getting a certain weapon in a drop are dependent on a number of things, including; the desirability of the weapon, the weapons you already have, and, perhaps, how long you have been playing, etc. For example, the system might award you Suros, but then your having Suros would cause RNG to decrease the likelyhood of you getting Ghorn. By doing this, it would be possible for anyone to get all of the exotic weapons, but it would be more likely for a player to always be chasing at least one of two of the most wanted weapons. Just my 2cents.