>>51516159Fighting/Dark is phenomenal offensively. It also has the coverage moves against Fairy types.
Water suffers from the signature move being a 3-hit move, making it trigger Rocky Helmet 3 times. It can't pass through bulky Grass types like Tangrowth or Amoonguss that don't have a Fighting weakness, or common bulky mons like Toxapex or Slowbro.
So the key here is that most fat fucks don't resist the Dark, signature crit move, while they resist the Water move.