Sadly, this happens all the time. I have buddies who join in at the end of raids and get the only exotic drop. It's kind of a joke in our team now that when someone comes in late and especially if they do nothing, they will get the greatest reward. We all laugh about it now. Happens in the crucible as well. Playing with a team the last few nights and one guy was always on the bottom of the team and every time except once, he was rewarded. That is out of several hours of gameplay. It wasn't anything great that he got but it was just the fact that he kept getting something every time. You just have to laugh about it or you'll drive yourself crazy.