Guess what, its not. They didnt have the idea, they used the idea someone else already did. Only difference is, the other people did it first, did it better, and are still doing it...daily.
You can literally make as many items as you want. Charan and Reaper have made over 3 themselves that are already in game. Thats right, ALREADY IN THE GAME. And its not even released yet. They also have another 1(Reaper) and 2(Charan) coming into the game soon.
I also have a weapon in the game already. You think Blizzard is genius? Try again. They took over a year for an idea that their more successful opponent has already been doing for a year.
Also, just so you know, out of their impressive list of over 180 uniques or legendaries, almost a third of them are player and contributer made. Meaning at least 50 different weapons, armour, and other various in game items are player made. Already in the game.
Let that sink in...these items, that non dev players created, are already obtainable in the game.