The only time I'd use a King's Rock is in a 2-on-2 match with both Pokémon using moves that hit both opponents to maximize flinch potential.
Good players will almost never rely on luck to win their battles. They may attempt to outpredict their opponent or throw in some random factor that can make things difficult for the opponent - but they won't let luck have the opportunity to become their opponent as well. They want their side of the battle to have factors that they can control.
That said, dump that Crobat set immediately. Go for a Choice Banded set with Sludge Bomb, Shadow Ball, Aerial Ace, and Hyper Beam\HP Ground or Rock.