So there's a glitch that you might not get powerful gear from the weekly challenges that just reset (the vanguard, Gambit, and crucible ones). From what I can tell whether or not you get powerful gear depends on if you did that challenge before the mid-week reset. I had not yet done the heroic story missions challenge, and I got a powerful item from that, but only got 500PL items from the rest of the challenges. Bungie please fix, it probably has something to do with the system not recognizing the mid-week reset and denying powerful gear because people already did the challenge earlier in the week.