Relative to their size, their bite force is rather average. It's been measured in several different breed tests and pitbulls simply don't have the bite force idiots like to claim with zero research. Their bite force is measured to be less than half that of the strongest breeds.
And tenacity is the most hyperbolic attribute you could possibly define an animal. Oh it's real tenacious because you heard of a story about how your 70 year old Aunt couldn't beat one off during a fight. So tenacious.
There's a reason vets and the kennel associations aren't the people with some vendetta against pitbulls. It's ignorant people who heard from somebody who heard from somebody.
It's funny you keep mentioning retrievers and how soft mouthed they are. This family pet must have gummed this 4 year old to death a few months so.
https://m.news24.com/SouthAfrica/News/boy-4-killed-by-family-labrador-in-horror-attack-20160817