Why I always lose in PWT (Pokémon World Tournament)?

I use Serperior, Ninetales, Golduck, Sandslash, Joltik, and Unfezant in Triple Battle on Kanto Leaders; and I always lose in a tournament. Using items from the bag is not allowed and only using held items. Several (but not all) legendary pokémon are banned in that tournament. Why I always lose in PWT (Pokémon World Tournament)?