Sorry as the owner of 2 Great Pyrenees I have to agree with CASDOG1 and MrsBacbach. As said their size and all that hair, especially around the neck is so they can fight off multiple predators and they do not fold. They. Do. Not. Fold. Against any threat. They are relentless. I have seen them go into what I call "ballistic mode" over anything they perceived as a threat and that includes humans.
But they are so intelligent they know when intimidation from their barking is enough to deter a human and when they need to amp it up. Maybe you have seen some GP's that would back down from a human, in all breeds there are exceptions, maybe mine are the exceptions.
But I can tell you there have been multiple occasions when my 2, if not for the fence would have happily "tag teamed" a human that they perceived as a threat. Tag teamed...it is almost as awesome to watch as a good herder. It is why I keep TWO. As said, the only thing that would have stopped these two would have been a gun.
My property is fenced so my two won't become "disapyrs" LOL and I have considered that limiting their area to an acre with chain link fence has amped their guarding intensity...I don't know. I do know that whatever they have decided to guard...they will protect with their life. As witnessed the day a bear ran through the field by my house. I thought the fence wouldn't hold them that day as they were backing up and making a run for it. I think only the fact that I was standing there trying(that being the optimum word) to defuse the situation kept them from going over the fence. They, however, continued to patrol that fence long after they had calmed down. Never underestimate a Pyr. I saw them in action that day and even though I knew they could move when necessary...I was astounded at their speed and agility. I am sure they would employ that same speed and agility against a human they decided was a threat. No doubt in my mind.
All that said, I have owned a German Shepherd/Rottweiler mix and she was willing to take on all comers animal and human, her ONLY fault was she didn't seem to know how to distinguish the difference as well as my Pyrs. Her guarding/nurturing instincts were unbelievable. She was a "one in a million" dog. I've never owned Dobermans but have had family who had them. I know they have run coyotes off the property and I know/have witnessed their loyalty and "heart". I would not want to see a Doberman tangle with a bear. I have no doubt they would try. Just as my Rotti/Shepherd mix would have. I don't think it would end well. I have owned rescues/"mutts" of various types that were exceptional dogs. Any dog can be exceptional that is bonded to you even if their bred in instincts pull them one way or another.
Sorry I rambled. I just HATE to see GP's underestimated. Or any dog for that matter. As the saying goes, "it is not the dog that is in the fight, it is the fight that is in the dog". Create the relationship/bond with your dog and watch them rise to the occasion whether they are well suited for it or not. That is what makes dogs dogs.