While Nixon was caught with his hand in the cookie jar, it seems like politics used to be more corrupt in general, in that era and before.
It’s difficult to meaningfully bribe the general populace. Vouching to lower taxes is about the best you can do. If you just need to convince the party head that you’re the person to choose, then all sorts of backroom shenanigans are easy to arrange, and so they did and so we had lots of corrupt leaders. Moving back to party-head selection process would likely mean a return to general corruption.
Superdelegates are probably also prone to fall into the bucket of corruptible entities, in the long run, even if they aren’t yet.
The Venetians had an elaborate system of electing the Doge that used several steps of randomness to try and ensure that no one affiliated with anyone was making the decision, and you couldn’t predict who those people were, so you couldn’t bribe them. And that system ended up becoming corrupted because, in essence, while selecting random people as the electors, they were always random people from the nobility - and the nobility had become a corrupt class, in general, so they tended to pick people who would continue to make that more easy.
It seems that Clinton did, effectively, buy the election within the party. More than them pulling some clever moves to hurt Bernie, her ability to finance the party made it impossible for other candidates to step up to run against her, despite Hillary having been an unpopular candidate that most anyone could have won against if they’d been able to. The party decided that it was more useful to have the money to use on Congress than to have a strong candidate.
That had nothing to do with Superdelegates. Clinton won more because no one else ran against her than because the Superdelegates backed her. There should have been more names in the race than just Clinton and some Socialist crank. But even were that not the case, Superdelegates would eventual become a target for bribery and corruption.
Democracy, on the other hand, while hard to corrupt - unless you’re narrowing it down to sub-sections of the populace, which you can do given enough time - doesn’t really prevent corruption either. And, more importantly, it promotes Demagogues. Which isn’t to say that a Demagogue is bad. Julius Caesar was, at the end of the day, a clever guy who knew how to get shit done.
But consistently finding a good Demagogue is hard, and even the best of us will go downhill at some point (read about the last years of Madison’s life, for example). Many a great leader has screwed over his legacy in old age, unable to recognize that he’s no longer the man he was. Nepotism, in particular, is a factor that seems to be very hard for even the wisest people to avoid. While doing everything else smart and canny, they’ll then go and put in their idiot son as their successor.
Caesar was great, and the people loved him enough to force the country to abandon Republicanism, when he was assassinated by Senators, trying to protect the country. And that choice sent Rome into a downward spin that never corrected. It was all downhill from the moment they abandoned the Republic, despite each Emperor having full power to do everything necessary. And that’s counter-intuitive to your average person. Endless bickering, compromising, and taking half-measures by a Congress of people can’t possibly be more effective than a powerful, capable leader with full ability to make any decision necessary for the state.
But no, reasoned debate by a Congress of educated people is more successful - particularly in the long run - than rule by a great leader.
A single voice to try and give some shape to the debate is good. Rule by only a Congress would be hellish. But it needs to be a balance, and most people don’t respect that.
What’s needed isn’t democratic election, superdelegates, or historic processes. Something new needs to be developed that is able to find decent people and vet them.
I suggest a solution that treats it like a job. Not a campaign, but an interview process. And I mean that on the side of the electors. They should be finding candidates and taking them apart.
Don’t just select the electors randomly, make sure that they represent all of the people of the country, but also are reasonable-minded sorts within that class. But beyond that, they should be random and unaffiliated with the party heads in any way, direct or indirect.
If we still have a democratic general election, then ask them to promote a few names so that you can have an in-party election of those candidates, to make sure that the candidate can win a popularity contest - something unlikely to come out in an interview.