A few points...
Dogs do not live in packs. They live in social groups with no rigid hierarchy or clear leader. They'll often leave one group and join another. Pack theory was based on a study by David Mech. He observed a group of non-related, captive wolves. None of the behaviours he observed such as the alpha roll are seen in wild wolf groups who live in family groups with the breeding pair taking the role of leadership. Pups do not challenge the breeding pair for leadership. Mech himself has admitted that his research was deeply flawed.
Also, dogs are not wolves. Wild dogs behave nothing like wild wolves. They're also very aware that they are not human and humans are not dogs.
The XL bully is not a recognised breed in UK. It is a mixed breed.
The breeds they were created from were historically bred to be gentle towards humans. They were used for dog fighting and bullbaiting and needed to be handled by people when in a state of high arousal. This meant that any dog who showed aggression towards people was not bred from.
Of course, more recently a certain class of people, mostly young men, have sought to deliberately breed aggressive examples of the breed. That has no effect whatsoever on the responsibly bred bull breeds who maintain their gentle nature.
Breed-specific legislation has done precisely nothing to reduce the number of fatal dog bites. Banning these new mixed breeds will also do precisely nothing to reduce the number of fatal dog attacks. The young men who breed and own them will simply move on to another breed just as they did when the pitbull types were banned.
The answer to reducing the number of attacks lies in the control of breeding and education. Ban backyard breeding completely. If someone's dog accidentally gets pregnant make it illegal to sell the puppies for profit. Ensure all breeding bitches and dogs are licensed and have the relevant health and temperament tests.
Educate people on canine behaviour. Attacks rarely, if ever, come out of the blue. Dogs give many, many warnings before they bite. The problem is, unless this warning is a growl, which is the dog's last line of communication, most people don't spot the warnings.