The notion of "superdelegates" is inherently anathema to democracy. Every vote counts equal. Introducing a class of people whose votes are worth more than others inherently corrupts the process. Since the superdelegates overwhelmingly supported Hillary, they gave her an unfair advantage.

Hillary won against Bernie because the deck was stacked in her favor. Of course, she didn't have any sort of unfair advantage in the presidential election, where she proceeded to lose against Trump, of all people. Because she couldn't rig that contest.