What makes a protagonist a protagonist isn't how extraordinary they are, but rather the fact that they stand at the very center of the story, coupled with their uncanny ability to make things happen.
The reason Harry and his companions could play this role—aside from the fact that Harry was Voldemort's destined nemesis—was that he used this very status to set off a chain reaction of one story after another.
If Harry hadn't managed to hold his ground and had simply been snuffed out by Voldemort in their first encounter, he would never have survived to anchor the subsequent chapters of the saga.
Chapter 387