May I respectfully suggest that the early reaction to Harris suggest that this is an utterly irrelevant question that can be parsed and dissected a thousand different ways that will all lead to the same conclusion: so what?
Whether you think that Biden was “popular,” whether or not you think he was treated unfairly by those who advised him to drop out, whether you think he would have beaten Trump or not, it’s moot now. Biden isn’t going to be the nominee, Harris is.