No this is how it should work. Exotics are getting way too easy to obtain over xur. I remember when early on i once saw a guy with monte carlo and o followed him around while drooling all over thay gun. It should work like this. Xur comesto the tower and bring an exotic weapons engram which you can buy only once per character. This would give you a greater chance of getting the exotics that you want while preserving its rarity. And dont forget that those engrams would be divided into primary special and heavy. And theres only 4 heavy exotics that you dont obtain trough a bounty.