We traveled on the Grand in August and were in an AB mini suite on the Dolphin Deck. We loved it ! Yes, they are exposed to the cabins above but we never had a problem with privacy. Most who book a balcony cabin enjoy their privacy and respect the privacy of others. We really enjoyed the Dolphin Deck, which is the lowest deck, becaus we could sit on our balconies and enyoy the ocean, almost at eye level, without any obstruction.
I can't provide any info on the balconies on the other decks but can tell you we really enjoyed ours! We too had reservations about the balcony being open to all above but truly never had a problem even though the Grand was filled to capacity.
Feel free to email me if you would like more info.
Most of all, enjoy! It's a great cruise.