There is no one answer to this question as it depends on the breed of dog and its individual characteristics. Generally speaking, purebred dogs are more likely to be good at agility than dogs that are not purebred. Some dogs are simply better bred and have more of the genetic traits that make them good at agility, while others are specifically bred for agility and have been specifically trained to do so. Ultimately, it is up to the individual dog owner to decide if their dog is good enough to compete in agility.