Biden does have some strengths against Trump that Hillary Clinton did not. We mock his his rambling and tendency for “gaffes”, but these do mean he never sounds like a “scripted politician.” Clinton was criticized as robotic and focus-grouped. Biden is anything but focus-grouped; whatever pops into his head comes out his mouth.
At the same time, compared to Trump, Biden has:
No voter enthusiasm
No real argument for himself
Ask yourself: how likely is such a candidate to win? Is such a person really the one you want to run against Trump? Look at the enthusiasm Trump gets at his rallies. It is real. Trump has fans, and they’re highly motivated. How motivated are Joe Biden’s “fans”? Is Biden going to fill stadiums? Are people going to criss-cross the country knocking on doors for him? Say what you want about Hillary Clinton, but there were some truly committed Clinton fans, and she had a powerful base of support. By comparison, Biden looks weak, and Trump is savagely effective at preying on and destroying establishment politicians.