Although a defector is not a temporary student or H1-B, yes it is complicated but you are saying there is no cause for concern even though clearly Soviet citizens would not have been allowed in such high numbers into important roles and I suspect people would rightly question the numbers if nearly half of all STEM graduate students were Russian right now.
I call it a caste deliberately for those reasons. It is hereditary I believe whether through socioeconomic status or genetics or culture or legacy status. It's already becoming apparent. There may or may not be social consequences. I fear there will be.
H1-B visas didn't even exist in the 1940s. I don't know what the immigration system was like back then, except that it was fairly racist (this is before the reforms in the 1960s).
Most of the foreign-born STEM graduates I've come across in the US are not from a hereditary caste. I'd even say most of them are from the first generation in their families to obtain such a high level of education.
Legacy is something very different. It pertains mostly to undergraduate admissions at elite universities, and almost by definition, foreign-born students are not the main beneficiaries.
I call it a caste deliberately for those reasons. It is hereditary I believe whether through socioeconomic status or genetics or culture or legacy status. It's already becoming apparent. There may or may not be social consequences. I fear there will be.