You're wrong.
Many XL bullies in this country are very likely related to an XL nicknamed killer kimbo.
I'll let you guess why he's nicknamed that.
When these dogs were being selectively bred by humans the gene pool was condensed and a lot of behavioural issues in this breed of dog are because of the characteristics this dog was bred to have like the bite with a super high pressure and rear facing canines for that slicing action, and an innate lack of freeze or flight fear response, and the standoffish attitude which makes it a perfect status dog. Those behavioural characteristics don't suddenly change if you're an elderly woman altruistically rescuing one, or a mother of young children wanting to show the world that these beasts are loveable giants, or a genuinely good man who tries to see the best in all animals and really deeply to his core believes there are no bad dogs, just bad owners because he bought into Don Bluths all dogs go to heaven a bit too hard during his childhood.
Yes, other dogs have killed. It's true. Some of those dogs were bred for killing, terriers kill rodents, they've killed babies. Other large dogs have shown behavioural issues and their owners have had rose tinted glasses about their behaviour and it turns out they've had brain tumours or their lineage shows an excessive amount of inbreeding. We never have answers for some dogs.
It's not the fact these dogs were lockdown dogs, or that they have bad training. Many of these dogs will have had perfect recall, an affinity for obedience and learning, and have been highly respectful of their own families dynamic... until they weren't.
Once it's in their genetic makeup you can't just train it out of them.
You can't stop pointers pointing or retrievers retrieving, you can't stop XL bullies having the inclination to attack, even if that's not what they were bred for, it's part of them now.