Any way you get an exotic in this game is by the means of earning it. If you buy something from xur, it's through the means of strange coins. You had to do a tedious strike to get the coins, therefore you earned the coins and you merely redeemed the weapon in exchange for the earned coins. If you get an exotic from a legendary engram, you had to kill an enemy to get the engram. No matter what means you get them by, you earn your exotic, unless you're one of the cum guzzling f*ggots who afk vanguard strikes and get good shit out of it