I have no problem with it, a Battleship fleet will do around 0-2 damage on a army or tank group, which cost me maybe 0-50 to repair, I then attack him with an air fleet and do 2-5 damage and sustain 0-2 damage, that will cost him allot more than it cost me. He will have to go back to port and retool and repair the damage.
So all in all, using your Battleship fleets to attack ground targets is not such a great idea, just as it was in real life.
Though, you shouldn't be able to destroy a land unit with either naval or air units in my opinion anyway.