I'll be honest, I haven't sunk hours into the cave but I have done it and it really hasn't been to my favor. Only a handful of legendary engrams and they all turned to rares. Even the rares I've gotten, I haven't really replaced any of my current load out with any of it. So I guess, for me, it's just been leveling my Cryptarch rank. You may have a point when it comes to the Iron Banner but the people who are -blam!- this spot are pretty low lvl players. Unless I'm in the minority and people HAVE been getting some really epic drops...