If there were dogs that could fight as well as a Pitbull, their breed would be called Pitbull, and Pitbulls would be called something else. Pitbulls are Pitbulls because they represent the premier line among dogs in combat, whether against other animals or other dogs. A dog of another breed needs to be at least twice the fighting weight of a Pitbull even to make it interesting.
I wonder why I don't constantly hear advocates for their breeds insisting that their favorite breed would actually beat a greyhound on the race track. Greyhounds aren't the dogs on the race tracks because folks just think they look right running on a race track, or because of some cherished tradition. They're there because they represent the premier racing dog. Same with Pitbulls vis-a-vis combat.
