I am going to say no to your first point. I'm also going to ask how many aggressive dogs you've actually worked with before, because what I'm saying is coming from actual experience.

I have never once witnessed a dog become a biter from the methods you describe. Most dogs are not predisposed to biting outside of play. They will mouth you, sure, but they won't bite aggressively.

The reason for this is there are a couple types of biting.

The first is fear biting. This can be taught, but the dog gives ample warning. Dogs that do this have mostly learned to be afraid, and for the most part, it's fixable.

Then there's food aggression, which is 99% genetic and fixable to a limited degree.

The third kind of biting is different from the above two because the dog gives no warning. This is an extremely dangerous behavior. It is not taught. I have seen small puppies exhibit this behavior, and every dog I have ever seen that exhibits this behavior has done it their entire lives. Most of them were in homes with other dogs that behaved appropriately.

Had OP's boyfriend wound up with another dog, it may have become an annoying pest, but unless it also had this tendency I doubt it would have bitten. One day in which the dog was exercised, but no one came over the house or pushed the dog is not proof that the dog's behavior was in any way better. Even if it was, congratulations, you've just moved the boundary and made a more unpredictable dog.

I know someone who has a dog like this. The dog was raised properly, brought to all the right trainers, and has boundaries. The dog has bitten three people and cannot be out when people are over anymore.

This is a genetic issue almost always.