That is a pure speculation with frankly not a lot going for it. An equally plausible, if not more so, hypothesis can be made: People generally do not like bullies, and especially in this cycle the anti-establishment sentiment has played a big role, as observed from both parties' primaries. See Republican process and how The Duck profited from the anti-establishment sentiment. Sanders likewise might have benefit from a similar electoral mood, which explains his rapid rise - his rise is arguably bigger than The Duck's, considering the latter's name recognition in the national stage.
Then you tell me, what purpose has the overwhelming level of early endorsements served? And I don't just mean those coming from the AP investigations, since they were just answering a question, but all the superdelegates who have made public statements supporting Hillary. When is a political endorsement by a politically relevant person not made with the intention of bolstering their campaign?
Or did they just all choose badly?
Again, if one contests the idea of closed primaries as undemocratic, then equally strong, if not more so, charges can be made against the closed caucuses where a tiny minority of activists cast the lion's share of votes. And not every primary is closed to party members. So it is difficult to say who benefited more from the process.
They should do away with closed caucuses too. And I never said every primary was closed, it doesn't have to be across the board to have an effect.
What is certain is that both candidates participated in the process with the knowledge of the rules and settings. I do not think it helps anyone complaining about the rules at this point.
If you want to have the slightest sliver of a chance of becoming president you need to run with one of the two parties.
So long as these two organizations have such decisive control they should absolutely be open to criticism when their rules are not inclusive enough.
Ideally I'd prefer the voting process was completely overhauled into something more like STV, but then there wouldn't be a need for primaries at all and the parties would lose a lot of traction.