The first curse is an exotic bounty in which you get a common grade test gun (Imprecation) from Banshee at first and in the end it should turn into the first curse. If I'm not mistaken Banshee also had a hand in the pocket infinity bounty. So it is quite possible that bungie has followed that theme of upgrading a gun in these banshee related guns. I understand the train of thought about it being unfair because not everyone has it or chose to do that quest. But if we remember Bungie's position on ghorn drops, unfortunately some have to be the unlucky few thats just how it goes. And with that in mind, it is still possible that they couldve went down the road of using pocket infinity as a base.