I don't think anyone is confusing Joe Biden as a perfect candidate nor a perfect human being. Geeze, who among us hasn't changed from what we were 30 years ago? I get tired of rehashing ancient history through the lens of today. It's meaningless unless the person involved has shown no hints of evolution themselves, and that isn't the case with Biden.
Whatever Biden did in the past, he made his bones by being the faithful partner of Barack Obama, and people haven't forgotten that. You undermine your own case when you claim that somehow the folks in South Carolina changed the minds of everyone else all by themselves. Joe Biden was going to win in SC even if Jim Clyburn had not opened his mouth, though I'm sure in lesser numbers than he did with Clyburn's support. He was going to win because Uncle Joe was in the pews and sanctuaries of SC black churches while Bernie avoided the state like the plague.
Bernie's fatal mistake occurred in 2016 when he was first building his coalition. You are absolutely right, Bernie was actually there in Selma in 1963. He was a champion of civil rights, but he shunned his connection to the black community - particularly in the South - to chase white working class voters with his populist messaging. Many of these voters viewed civil rights and racial disparities as anathema to their own interests and emblematic of the federal government's overemphasis on grievance politics for every segmented community but for their own.
Black Americans, particularly black American woman are the backbone of the Democratic voting base, period. Imo, this is why Kamala Harris is going to be Biden's VP choice, which he pretty much telegraphed blatantly the other day. Join this sector with white suburban woman who are incensed by Trump's ignorance and misogyny, more mature voters and all those conservatives, moderates and independents chafing to remove the yoke and dysfunction of Trumpism once and for all, and I see a coalition very much like the blue wave of 2018 that swept a diversity of Democrats into office all across America regardless of their individual personalities led again by a record number of women candidates.
As I said, 2020 is an unmistakable referendum on Trump, and his glaring ineptness and narcissistic incompetence grows each day as this pandemic rages through our society. By November, Trump wouldn't be able to win an election for dog catcher as it looks. Reality will help defeat Trump more than enthusiastic support unable to be massed in the social distancing constrained streets and squares across America.