So, first of all, if you drew up a list of highly successful people in mediaeval Europe, I don't think there would be many Jews there.

Secondly, I take it you have in mind Cochran's theory that European Jews are super-smart because of evolutionary pressure from mediaeval persecution. But Cochran's story isn't simply "they were persecuted, persecution leads to more brains, the end". It depends crucially on the details of the persecution. And the treatment of black slaves in the US is very different in pretty much every relevant respect from the treatment of Jews in mediaeval Europe. The Jews were forbidden to do many jobs but highly lucrative finance was (for bizarre path-dependent reasons) open to them; black slaves in the US were given backbreaking physical labour to do and had no opportunity to choose their work. The Jews were left more or less alone much of the time but subject to occasional slaughter where the best opportunities for survival went to those who anticipated trouble, had accumulated valuable resources for escape, etc; black slaves in the US were subject to constant low-level mistreatment and occasional individual murder, and opportunities for getting the hell out were ... limited. European Jews, Cochran suggests, had very little inward gene flow; female black slaves in the US were routinely made pregnant by their owners, and I'm pretty sure the children were generally (1) also slaves and (2) considered black.