Suppose, hypothetically, that human brains were such that IQ was capped at 145 ... it would look like the correlation between IQ and real world outcomes vanishes after 145

In your hypothetical there would be a lot of warning signs -- for example all IQs above 145 would be random, that is, re-testing IQs above 145 would produce a random draw from the appropriate distribution tail.

And I suspect that it should be possible to figure out real-world distributions (the fatness of the tails, in particular), by looking at raw, non-normalized test scores.