My example is ridiculous, but it was the easiest way to point out the fallacy that "you can never measure which [immigrants bring value or cause problems]. You clearly can.

And no, that 68 year old alcoholic is free to pass into America under Democrat administrations and tens of thousands have. They technically are illegal, but if you selectively enforce immigration laws and offer things like asylum/refugee status without any checks or balances, the net effect is still the same.

Returning to Japan, as the other commenter pointed out, your PhD example is someone that qualifies for expedited permanent residency, a particular subset of migration that Japan has (correctly) decided to encourage.