Three things.
1. Kavanaugh wasn't properly vetted. He ought to have been in the normal way for SCOTUS candidates. That would have saved everyone from the mess. In the US system, presidential candidates are vetted in a totally different way: by public examination. [I've mentioned previously that I think parties should vet candidates before putting them on the slate, but that's idealism in the US free-for-all system]
2. You may remember that my position on Kavanaugh was similar to the one Republicans took on Clinton. It wasn't what he did, which to me was just a bit beyond the sort of drunken behaviour plenty of sexually excited/ frustrated kids do. He could have found a way to explain such an event so long ago in a different era. It's that he appeared to me to lie about it and the circumstantial information surrounding it. I see no reason to suppose Biden is lying.
3. Given the reluctance of the witness, her evident trustworthiness and K's lying, there ought to have been an investigation of K. It wasn't about putting him in jail. It was whether he should get the job for life. But 1 and 2 are not true for Biden so 3 doesn't apply either.
So I guess you are working the double standards/ hypocrisy angle I predicted. But the situations are different.
As regards accepting whether the allegations of a pattern of behaviour are true, it depends whether you mean the court of public opinion or of law. The phrase I'd use as a non-juror is that my presumption is that people who are accused by multiple accusers of the same behaviour are highly likely to have done it; but the accused may produce evidence rebutting it. If it's persuasive, I will listen. In Trump's case, of course, he lies every time he opens his mouth, but admitted on camera exactly the behaviour he was accused of (grab them by the pussy).