Even though Xur is cheap you still have to earn strange coins from nightfall or weekly's. That or get one at a time from breaking down engrams. On the flip side of the coin you can get an exotic from a legendary engram from a lvl 2 dreg or you can complete raids or strikes for a better chance at them. Even exotic bounties you complete tasks for a certainty of obtaining that weapon. So yes everything you obtain in this game you technically earn. It's just that some items you will get were more easily obtained than others because of sheer luck. It's RNG baby. It's all luck.