It's neither impossible nor possible. Strength in a dog varies from breed to breed, and dog to dog. Speed and agility can also make a big difference. German Shepard are intelligent dog's, but asking whether or not they'd take out any breed is hard to say. They're Loyal. It also depends on the situation. Some dogs have been known to kill bears, and even wild cats and armed robbers to protect their owners lives. Against a pitbull, a rottweiler, and an american doberman, I don't think it would have a good chance. They're not fighting dogs, and they're not meant to be challenged as one.
Although a German shepherd could be ferocious, I think it would have a hard time with a rottie and a doberman and possibly a pit bull. A rottie weighs more than a shepherd and is stronger. A doberman and a pit bull would be a tough fight. If they can all bring down a man, I'm sure they would all be a challenge to a German shepherd.
I don't think so. I have a German shepherd and a Pitbull. Occasionally they fight and my pit bull always pins the German shepherd... Don't get me wrong the German shepherd is the most loyal dog that's for sure!!! Very agrresive towards people whenever owner (me) is around.