I'd be more inclined to think we'd relate to the person who talks and acts like a regular person. Even in a TV show Elizabeth would be the secondary character. Is that because she's less interesting, or the writers are morons who don't understand which of their own characters are compelling? Not at all. It's because super colorful characters don't work as the main protagonist. See again--River Tam. Comedy needs a straight man, and drama needs one too. Everyone liked Jack Sparrow better because you were supposed to--but as evidenced by the later movies, he couldn't carry the plot by himself. As uninteresting as he seemed, the Pirates movies needed Will Turner to work. Characters like Booker make characters like Elizabeth possible.