I bought I think four weapons from Xur, ever. Truth, MIDA, Ice Breaker, Red Death. Ended up getting MIDA, Ice Breaker and Truth as drops later on. Red Death is the only one I wouldn't have right now if Xur wasn't around. When it comes to armor however every single piece has come from Xur as a buy it from engrams. The only armor I get from Nightfalls ends up being for other classes, or I get a piece that I've already gotten from Xur.