I can't comment on that specifically since I have a great personal dislike for Biden but looking back at the other candidates I don't really see anyone else who could have done much better against Trump (and no, Bernie isn't it either, nor is Cuomo or whoever). The biggest challenge for Democrats is that Trump can make anything up and his 42% base seems invincible so he can just keep throwing shit at the wall and wear his opponent out.
Eh, maybe. But I don't know how much we can trust the early national polling regarding democratic candidates. It's not really something that makes a lot of sense.
Biden had one of the worst enthusiasms for a candidate in polling, among many of the others. I guess with my line of thinking we could also write this off -- I just don't see people in my life that are big Biden guys. He doesn't have much of a following and has been highly absent in the media recently. It's all eyes on Trump now, for better or for worse.