I'm noting that expecting people to vote for the least bad candidate here is easily rectified by the Dems choosing someone less terrible. The base would vote for a pickle sandwich if it had a blue sticker on it. As such, choosing someone who appeals to swing allies is the right move.
Biden, whatever value he has, does not appear to have that appeal. So if winning is important, Democrats hold the key. Choose someone less repugnant to swing voters.