Your friend is probably right. His dog might not do the bite work. If it was only taught to be a pet dog it never got the right environmental stimuli to be a pm outstanding protection dog. Even though they are supposed to be natural guardians. But it was taught to look to humans for all of its needs. If a real challenge comes it might bark butt still hide behind the owner. A good trainer cam evaluate the dog and if it has enough potential can teach it to protect. 

https://youtu.be/8T-bEsBukPM

https://youtu.be/DuZIxjgwd98

Only a few dogs will actually protect if they are untrained. I've seen dogs from very strong Schutzhund lines that were afraid of their shadow. It's dam and sire were selected because of their working ability and having generations of good working qualities. Yet thy still produce dogs that do not have the correct temperament to do the work. By the same token there are dogs that can do the work. They didn't come from a long line of working dogs. They still have the correct temperament to protect especially when taught.