Lauren Alaina’s “American Idol” legacy can be summed up in one phrase: failure to meet potential. The Season 10 runner-up kicked off her “Idol” run with a fiery display of vocal talent, but she was never able to match that confidence or sense of identity in subsequent live performances. Worse yet, her “Idol” catalogue stood in stark contrast to that of winner and fellow country artist Scotty McCreery, whose best strength was his firm grasp of self.