Even if I bought as a general principle the myth that the way to win is to mimic Hillary and Kerry and Algore and Mondale, and running somebody more like what Bill and Obama claimed to be during their campaigns is the way to lose... I'd still have to notice how well this particular round is set up to go the other way anyway.
Not only has this particular progressive already been the country's most popular politician for years, with the highest favorability even with voters for whom he's not their top choice, and among almost all demographic segments, but also, look at who the not-progressive options are...
The guy who's literally trying to just buy his way in (including buying changes in the rules when he can't get in by the original rules) after having previously always supported the other side and thus contributed to the situation we're in now, and reacts like a deer in headlights when he's confronted for the first time in years by somebody he hasn't already bought off?
The guy who can't remember where he is or what he's supposed to say half of the time, keeps flying off on crazy rants that have nothing to do with the situation, has a history of doing & saying stuff that most of the party's voters identify with the other party, occasionally takes a break from grabbing & pawing at little girls to grab & paw at a woman instead (although there was also that one time it was a man), has had no campaign activity of any kind in a Super Tuesday state in over a month, keeps making up serious "wannabe" stuff about his past, and bases his campaign on an implied endorsement of a disappointing former President who hasn't endorsed him and tried to talk him out of running, whose name he forgets?
The lady who's had several popular policy ideas in the past but also a history of flipping, whose campaign has been downhill since her latest few flips and her decision to make exactly the kind of ridiculous accusation that could have most easily been predicted to obviously backfire on the accuser, and finally ended up resorting to the same kind of "but I'm a woman (the only one in politics ever)!!!!!" theme that served Hillary so well and is currently doing the same for her?
They guy whose claim to fame at first consisted entirely of being openly gay but has now come to include either willingly & deliberately or just obliviously participating in a city-wide racist conspiracy at the behest of his big-money donors, who does a more surprised & angry-looking version of the deer-in-headlights thing when challenged, whose response to the issue of where his donations were coming from was to create a donor contest that was really transparently an attempt to fake better donor statistics, and who has never had more than a few percentage points of support outside of a few pockets of exceptional whiteness?
And that's without mentioning something they have in common (except maybe Warren to whatever extent), which is that even their own supporters generally don't really support them for who they actually are or what policies they actually propose, and can't come up with a reason why anybody should vote for them beyond "well you just have to settle for this mediocrity anyway". ("Like I did", in Mrs Biden's case)
Even if this bunch were the current representatives of a group that's more likely to win as a general rule, these particular examples of that group would be the ones who find a way to let it down anyway.
