@Lynn McGeein To speak to the point of the size of the dog, what I am saying is simply that the statistics you used are skewed because they do not take into account the fact that pit bull ownership is quickly on the rise in general. More dogs equals higher percentages in statistics regardless of the actual temperament of the dog.
A Chevy Silverado has one of the highest vehicle death rates in the US, but that does not make it an unsafe vehicle. There is simply a massive amount of them, everywhere causing a rise in the overall stats (this point was made with Honda Accords before, but that stat has since changed).
I understand that your insurance company restricts certain breeds and we cannot get around that. Unfortunately, we live in a world of over generalization towards humans, animals and things. This can be changed over a long period of time, but there will always be that one "scary" type of dog.
If your insurance allows and you allow larger dogs in your rentals, then there is absolutely no reason to restrict certain types of dogs. If you're doing decent screening and have pet requirements (deposits, insurance, trainings, introductions, et al) in place then your risk would be the same no matter if your tenant has a golden retriever or a pit bull. Bad dogs come from bad owners, and we don't want bad owners in our rentals no matter what.
I brought up the cow analogy to be similar to the Silverado one. There is a large amount of cows in the US, so they cause a large amount of deaths. Yet they are nothing to be afraid of.
Plus, a pit bull has a far lower bite rate than most smaller breed dogs. However, a bite from a pit will do more damage than a smaller breed, that's why the stronger dogs are on the list and the small dogs are ignored.
TL;DR: Over generalization is a bad thing. Dogs are as dangerous as you perceive them to be. Don't always trust statistics. You can't argue with insurance.