As the former head of HR at Apple said in the past but got fired for is that there are multiple forms of diversity and they have validity for particular reasons, however, to succeed as a business you mostly need diversity in thought (the opposite of groupthink), but there is also the social dimension of diversity which needs addressing if there are forces that are artificially affecting the dynamics.

That said, Japan, China and others have been very successful without having to import much external talent. And there are places with more social diversity than the US such have not done well, though there are examples of very diverse places that do extremely well too (Singapore and to a lesser degree Malaysia). So success is probably more aligned with economic policies and other policies weigh less.