I say you earned it either way. I know people bitch about buying the weapons from Xur but either way you spent time grinding away to get the weapon. Last week we carried a lvl 26 through nightfall and he was awarded with Icebreaker at the end. He told us it was his first time doing nightfall so basically for 2 hours of game play he "earned" Icebreaker. IMO he earned it waaaaay less than someone who got 9 strange coins from doing the weekly and 14 more through who knows how many hours of grinding. The only people I see complaining about Xur are people who were LUCKY enough to get the exotic they want as an award. It's funny how the second someone gets one as a drop they "earned it", as if the people who bought it from Xur did so by simply turning on their machines. I've not received an exotic from Nightfall but when I do I'm definitely not going to call for Xur's head.