Typing is useful but not a deal breaker. See: Tyranitar, Weavile, and Breloom on the bottom of this chart. All scary threats in both singles and doubles.

The real problem is giving retarded stat distribution and movepool. Aurorus is shit solely because of its stat distribution. It has awesome abilities, great STAB offensively and prime moves (power gem, freeze dry, -ate hyper voice). It's just supposed to be slow and bulky which is retarded BECAUSE IT HAS THE SHITTIEST DEFENSIVE TYPING IN THE GAME.

Typing helps but it isn't a deal breaker. Pokemon just need decent moves and decent stat distribution.