In fact, I think Klob might well be the ONLY other Democratic primary candidate besides Biden who could have won (Sherrod Brown also could have, but he didn't run). Her appeal to WWC and suburban whites in key swing states, especially in the midwest/rust belt, would have been critical. Any minor decrease in black turnout would have been more than offset by that, again except in GA.
I know her spiel was that she appealed to the midwest, but if she really did why did she get killed by Buttigieg in the only midwestern state where they ran (IA)? This, despite her being from a neighboring state and having the most extensive IA organization initially. ...unless you are arguing that she has an unique general election appeal to midwestern Rs and independents that Buttgieg doesn't.
Having said that, I do think she would have done better than Buttigieg in the general election, but thats more because of his negatives.