Quite apart from problems with the premises of this claim, the conclusion appears to be making the naturalistic fallacy – just because evolution occurs in nature does not make it morally good.
The Holocaust would appear to be an act of Artificial Selection, not Natural Selection (and therefore not evolution). Artificial Selection can select for any arbitrary trait, even ones that reduce fitness – as is quite frequently seen in dog breeding. Therefore the fact that they were subjected to the Holocaust cannot be taken as evidence that the Jewish people were weaker.
There seems to be a form of circular reasoning at work here – that they were killed is taken to be evidence that they were weaker, that they were weaker is taken as evidence that it was ‘right’ to kill them. The same logic could be applied to a decision to eliminate any arbitrary genetic trait, or genocide any arbitrary population.