Not many can pick up and carry a St. Bernard. However, I agree that one must be able to control one's dog. There is no flexibility there. If you are attentive and diligent you can train the dog without resorting to having to overpower it.

Speaking of overpowering, I used to walk a German Shepherd at a shelter many years ago. He wasn't well trained and in the beginning he used to tug at the leash with all his might. He was rather strong and not being dragged along was a good challenge for any adult human. This was despite the fact that he had only one hindleg. Eventually I taught him to walk without a leash. However, I will never forget him because he demonstrated to me how strong dogs are. It is not hard to exert control over them but if it has to be via physical means, it is not easy.