Heroes Don't Wear Capes
...But they fight with keys too big to fit into a pocket, much less any normal door. Hey, at least the chances of misplacing it are... slim (not counting the times he forcibly lost it, of course).
Sora may seem like your classical protagonist from any story, and to some extent, he is. However, unlike Riku, he didn't possess natural leadership qualities right from the beginning. Instead of taking initiative to build the raft that could potentially take them away from Destiny Islands, he sat around, being called a "lazy bum" by his friend, Kairi. It wasn't until he left Destiny Islands were he became more acquainted with his leadership abilities. For Sora, becoming a leader was a self-discovery; even though he didn't express it thoroughly in the beginning, it was always there.
However, a quality that does gear him towards the traditional hero archetype is his sincere selflessness. As he travels through different worlds, he willingly lays down his life in order to protect people who need protecting and sometimes--on the rare occasion--feel sympathetic towards an enemy. In a sense, his nobility can work like a double-edged sword by becoming his flaw. His priorities tend to shift around; though he keeps it in mind, he temporarily starys from his original goal. Though others view it as sort of a distraction, it is part of Sora's nature that he can't help.
Sora's role as the series ' protagonist takes a twist-- he isn't the hero in the sense that he's an adventure-seeking, action-loving fighter. His journey to other worlds isn't driven by the desire to wield power, but by honest intentions-- the desire to use power in order to keep others safe. Although he was somewhat upset that he found out he the "chosen one" selected by the Keyblade itself in order to wield it, he has not once complained about his obligation to save others.
His first goal from the beginning was to seek out his lost friends and return home safely. Thus, his ability to become the Keyblade master was not to vanquish evil out of pride or showing off his skill, but to protect the people who are closest to him.