Level design, and especially art testing, can be done by anyone with a brainstem. Art is the cheapest and easiest part of the game, because it's fungible. If you can draw a rock for Skyrim, you can draw a rock for Destiny. Art testing is so simple it could be done by children: "look around this thing and see if there's anything that looks stupid or broken"*. Because it's fungible, this means it can be outsourced to places where labour is cheap, like Eastern Europe. Actually making the game, on the other hand, is difficult, expensive, and must be done in-house. * they missed a few: you can see out the level just inside the first bunker on Mars, and there's a flying mushroom near where you spawn on Venus.