I've played for 400+ hours completed quite a few raids and night falls and no gally. Not saying I should have one by now but 2 of my friends have them with less hours. One got one with 100 hours on a nightfall and the other has 3 all from nightfall. Gally drops are luck and earning at the same time but some are luckier than others getting Gallys 100 hours into a game. I'd rather get a gally off a drop but xur selling isn't the end of the world I've played with guys that have 1000+ hours who just got theirs. It's all luck. Xur selling it wouldn't be terrible just everyone who thinks they're special because they are lucky and got theirs before others will be butthurt because a rng vendor sold the gun they "earned".