I think we're making mutually reconcilable points here.

> Quality is distributed somewhat evenly.

Starting from that assumption (which I can agree with), here is a simplified (perhaps numerically inaccurate) argument. Assuming the top talent constitutes 1000 best researchers who have just graduated from their PhDs, and all relatively equally qualified, 500 US, 500 foreign.

There are 400 postdoc appointments. Currently if 200 postdocs are US and 200 postdocs are foreign and these H1B rules then inevitably disallow the next generation to have 200 foreign postdocs we still have 200 US postdoc candidates who are just as good and are still top talent.

Would this not still retain equal quality?