I would suspect that the current existing high rate of genetic-based disorders among Ashkenazi Jews derives of course from such disorders’ presence in the very small “founding group” of a mere 350 people, but also due to a large amount of inbreeding (not breeding extensively outside the group) that has continued among them.
If there is one thing that human survival has appreciated it is genetic diversity, which is - genetic diversity - what many life’s species have succeeded with, for genetic diversity provides a greater chance of adapting to fringe conditions and/or new conditions.
Whether that 350 number is correct or not, the point you make has been widely accepted for many years. It’s one of the downsides of being Jewish. The upside of course is genius, and, in my case at least, great looks.
Simply a greater diversity of genes with which to improve overall resistance to disease is reason enough.