With respect, I think this is some pretty heavy revisionism. I can dig up PoliGAF peeps from before the primaries even began who were absolutely and completely confident that Sanders would only win a single primary. The average PoliGAF guess in December was two primaries (heck, I guessed eleven and was too low!). You cannot seriously be telling me that you think in 2014 you'd have pegged a candidate with Sanders' background and stances to do as well as he did. That's some bullshit.
It did catch a lot of people by surprise, though I think in the end it speaks more to the dynamics of an empty field than to Clintons weaknesses. Like, if 2012 was ron Paul vs mitt Romney, instead of a big field, Paul would have received way more votes than otherwise. The early branding of the primary as a boxing match by the media does a lot to legitimize the underdog and let them get airtime. Similarly, if you had Biden and Deval Patrick and Tim Kaine and a Castro brother in the primary, Bernie wouldn't have performed like he did.