The RNG system could work if they had implemented it better. Say like they had near the end of D1. Like when you rank up with a faction or in D2's case person you'd have a a choice between an armor engram or weapon engram. That way if you're trying to complete an armor set or just really need to get a better piece you have a better chance of getting it with the loot pool. Edit: this idea however wouldn't work for the gunsmith as you only get weapons from him and master Rahool as then if you had an exotic engram you'd be more likely to get the one exotic you want as currently you can't get cross class items(can't get Titan armor on a Warlock for example) and if I'm not mistaken the exotic loot pool is small (I don't know how many exotics are currently in game). But this system would work for all the other vendors.