People only rose to the occasion by chance. Had there not been corona and had the economy still been booming, Trump would probably have won. Surely it is possible to find someone out of 300 million people with the same qualities as Biden -- not a big ask, since his #1 quality is that he's not divisive -- but 30 years younger?
His #2 quality is probably having been Obama's Vice President. The majority liked Obama though to vote him in twice, and Biden represents more of that.
For democrats who chose him during his primaries, his #1 quality was that he was a moderate/centrist. The democrat party isn't only made up of leftists/progressives. There were a considerable number of democrats who were scared of Bernie and turned off by his supporters.
For GOP/Independents who voted Biden, his #1 quality was also that he was moderate and a close second was that he was not divisive.