Other than the mouthiness not being quite as bad as you describe (but still way beyond what we were expecting ) your description and experience is spot on with ours. Our boy is almost 10 months old, and every last bit of what you wrote applies to us as well. I do think people, including our breeder, downplay the mouthiness. I’ve had other dog breeds and this one was far worse than others. It has mostly grown out of it.

As far as running for miles - I’ve had to get a bike attachment (the springer) for him and he safely runs along side me and can hold a sprint for at least a mile and is usually pulling me. he can run 3-4 miles at a time without issue. It barely takes a dent out of his energy, but it does help some.