The link in the weekly update about the prophecy about the three of coins nerf brings you to a post from Cozmo about three of coins usage. In it he kinda makes it seem like we aren't using them correctly since he says something to the effect that the nine are pleased to see us blow the coins the way we were using them before, or that they will become more useful down the line. Makes OP seem like he's may be on to something with coins being needed on particular bosses to get certain exotics.