I can't see anything in your link that clearly indicates your position WRT clinton overwhelmingly winning open ones.
Wiki does not list open primaries, her win proportion of those, or the 'goal difference' in terms of awarded delegates. So - I'm not sure your statement is entirely true either.
The Wiki link lists contest type, winner and margin. It is very easy to compare and see how each candidate has performed.
The facts are, in open primaries Clinton has won 10-4. If you include semi-open it's 11-4. In closed primaries Clinton has won 8-1. If you include semi closed its 10-3. There is no meaningful difference. Sanders underperforms in all primary types.
The only contest type Sanders has performed better in are caucuses, winning 11-4. These are the least democratic type of contest of them all.
You're right that Overwhelmingly well was a massive oversimplification and exaggeration.
More accurate would be "appears to perform worse in closed primaries"
http://www.vox.com/2016/4/28/11528764/closed-primaries-berni...
https://www.bostonglobe.com/news/politics/2016/04/19/bernie-...
I can't see anything in your link that clearly indicates your position WRT clinton overwhelmingly winning open ones.
Wiki does not list open primaries, her win proportion of those, or the 'goal difference' in terms of awarded delegates. So - I'm not sure your statement is entirely true either.