If anything buying items is closer to earning them than getting a lucky drop is. Personally I dont really find either method if getting items to be "earning" since you cant actually actively try to get an item, if you want red death and it shows up in Xur's shop you didnt actually do anything to make that happen it was just luck. Also if you wanted red death and got it after doing a nightfall you still didnt do anything to get that item it was just luck. Really the only difference between the 2 methods is that when buying from Xur you have to save up coins so that you can buy the item you want if you get lucky and it shows up, where as getting an item as a drop is just luck but you dont have to save up anything in order to actually get it. Either way its really not earning, to me earning would be actively working towards getting something, for example the thing I find closest to actually earning is the Vex or Nechrochasm, where you can only get it one way and you have to keep doing that same thing to get a chance at the drop. Even that though is still not really earning since its still all luck as to whether or not you get the drop.