I'm a JDS fan, but how do you really dispute that the Cain fight did expose something of Junior's ground game? You can sit there and laugh at Mir, saying he couldn't find that out or saying that JDS showed that Mir has no stand up defense, but it doesn't take away from what the Cain fight showed us.
Cain will do that to a lot of guys, so I'm not ready to call Junior a fish out of water on the ground. He is supposed to be a black belt in BJJ from the Nogueira brothers, we definitely didn't see a black belt on the ground in that fight. I wouldn't say he has no ground defense, but I will side with Mir on the fact that the Cain fight did show us something about Junior's ground game.