Of the states that Bernie won, only seven were solidly Democratic-voting (Washington, Oregon, Vermont, Maine, Hawaii, Rhode Island, and Democrats Abroad). Five more are dem-leaning swing states, or were at the time (Colorado, Minnesota, Wisconsin, Michigan, and New Hampshire). The other 11 are solidly Republican: Idaho, Montana, Wyoming, Utah, North Dakota, Nebraska, Kansas, Oklahoma, Indiana, and West Virginia, and Alaska. If anything, it was Bernie, not Clinton, who overperformed in Republican-leaning areas.
That's largely because both the 2016 and 2020 generals, and the 2016 and 2020 primaries, were highly split along racial and educational lines. Black voters voted overwhelmingly for moderates in primaries and Democrats in the generals in all three contests, while white voters tended towards the more radical candidates in both primaries and the general (although the Bernie -> Trump vote gets exaggerated, it certainly existed, and his massive upset in Michigan foreshadowed Clinton's weakness there).
> Also because the Democratic primaries were objectively and transparently rigged.
Well, in terms of delegates, sure. But Bernie didn't win the vote, either. Clinton beat him by 12 points, not all that much different from the margin Biden was beating him in '20 prior to him dropping out.
> IIRC wasn’t Sanders polling better against Trump than Clinton? Then again most conceivable candidates probably would have…
The polling was a wash, ish, between the two. But of course the polling was also wrong in undersampling critical demographic groups that probably preferred Sanders to Clinton (although I'll note that Clinton won the primary in Pennsylvania, which she ultimately and decisively lost).
With the benefit of hindsight, maybe Democrats would have done a lot of things differently. (I certainly would have - I was so frustrated after Bernie lost that I ultimately voted third-party, although I might not have had I lived in a competitive state.) But certainly conventional wisdom at the time for virtually anyone in the know was that Trump was very unlikely to win, even as his popularity endured through things it never should have, and I don't necessarily blame them for mis-reading an electorate whose simmering frustration was suddenly at a boil.
My point being that Bernie being right does not mean he was, even with the benefit of hindsight, the correct electoral choice, nor does it mean there's some silent majority of Democrats who want progressive action but aren't voting for it.