It's pretty hard to define who's "leading" a team in a lot of cases, as others have pointed out. I don't think Rondo would ever "lead" a team the way a Bird or Jordan or Russell could, because he's not as good as them, and there's no shame in that.
But I think a guy like Rondo could be a major piece of a title team down the road. He doesn't have to be the best player on that team, because we aren't paying him like one, and title teams don't always have a clear #1.