Joe Biden is arguably a weaker candidate than Hillary Clinton; I can agree with that premise. However, the primary reason Trump is likely to lose this election badly is because of what he represents now versus 2016.
In 2016, his badness, his evil, his ineptitude, was theoretical. A large portion of the country warned against it, but it was still just a theory, a guess. There was still a glimmer of a chance he could rise to the occasion.
Now, four years later, his terribleness is no longer theoretical; it is reality. 2016 was an unlikable candidate versus a guess. 2020 is a more likable candidate versus a track record of evil doing.