Yes, because, while you might earn something through RNG because you completed a certain activity, it is still random. To buy a weapon from Xur you need coins, which you can get through RNG but also through completing a difficult weekly strike. (more difficult than normal strikes that is) This weekly strike does not have matchmaking so you need friends or other people to do it (or solo it if you have the nerve). Assuming that most people probably get their coins from the weekly heroic strike (seeing as you get 9 for a hard completion, 3x at max), you can say that these people earned the weapons they bought with these coins by either being sociable enough to put together a party or being dedicated enough to finish the strike alone. Whatever way you look at it, if we talk earning, then buying > finding.