I think the trouble with your stance here is the assumption that "rigging" is not the designed operation of the Convention.
There's no clause in the Constitution that guarantees voting equality in a party's primary. The primaries are run, each according to the rules set forth by that party. Superdelegates have been a part of the Democratic party's charter for quite some time now.
The Superdelegates provides a means for a level of centralized agreement when it comes to choosing a candidate. For example, if one of the potential candidates were a Totally Racist Underhanded Misogynistic Pig, the party can turn to Superdelegates to avoid that person from becoming the nominee. Think of it as a way to prevent hate and fear mongering from being the party message. They have a chance to exert some control over what SHOULD be a rational process, but can be easily subverted by a candidate that panders to the worst instincts of the people.
At this very moment, I'm betting the GOP wish they had Superdelegates, they might have been able to head off the disaster that is tearing their party apart.