Mate, the more you sink deep into this debate, the more i witness that you have tall words only and practically you need to be aware of many things still. Now that you have me stirring so lets get on about it.
Firstly you said that your dog is not used for fighting or hunting but its used as a guard dog. I myself have kept a Bully and Gulterr so i was initially interested in knowing that which technique have you used to curb down the Bully Vs Dog aggression?
You "socialized" this dog with other guard dogs. yes dogs learn from each other which is why when one dog barks at a stranger, the rest of the pack also barks.The replies from your statements indicate that you didnt use any formal training or trick or technique to curb down Bully Vs Dog aggression.
The temperament is attained from parents of the dog, which is why usually modern dogs used for breeding are of mild temperament so their pups can be trained in different ways. Good temperament pitbulls, rottweilers etc are used for breeding so the pups dont attain the aggression inside the breed.
Bully being a fighting breed has genes of a fighter dog in it. So you may not use it for fighting or hunting but still you havent trained it in a way not to attack another dog or wild animal, which it will eventually when it gets a chance.
To give you an example, ask a stranger or a friend to come to your gate and tell him to bring his dog also. Now see if your Bully is exhibiting more aggression towards your friend or towards his dog.
I have trained guard dogs also. The first command was "No" or "Stop" and the first training was not to eat any food from strangers. I hope you have trained your Bully in both because the command will save an innocent person or kids from getting mauled and bitten and the training will save the life of your Bully so it stays alive and protects your property.
Other very basic points to consider for a guard dog :
Have you trained this dog in attacking the arm of the bad guy instead of going for his leg or throat? The bandit can carry a weapon in his hands(not in his legs or throat) to endanger you or the dog.
Have you trained him not to be afraid of water thrown at him? or fire? or sounds of guns? or sound of heavy machinery or not to get distracted by high volume music? You do know that throwing of cold water is used many times to stop a fight between dogs.
Have you trained him to attain a grip through tug of war using a rope and cloth?
Now coming to your bet ;
GSD (German Shepherd Dog) has been a military working dog since past century, roughly 100 years or more. Its a search and rescue, explosives, mine and narcotics detection, handicapped assistance, messenger, police and military security dog and theres a tons of other work that a GSD can do.
Now answer one question only and i will take on your bet;
Which POLICE force or MILITARY Force is Using a Bully Kutta for above mentioned tasks instead of GSD?