You don't "earn" anything in this game. Nobody does. Everyone is at the mercy of the RNG system. Xûr may sell high quality things that make people who already had them feel like their time was wasted because they probably got it during a nightfall or a raid and then the next day he sells it, but let's face it. Xûr is the only guarantee about getting what you want. And nobody even knows what he's selling till he gets to the tower