Good arguments and discussion, for the most part!

However, the argument about IQ tests not measuring g seems exceedingly weak. Why don't you think g as well as analytic ability is impacted by nutrition and education and so on? Why don't you think that g is just analytic ability because that's really what correlates? Have you noted the difference between cross-sectional and longitudinal studies of cognitive aging? The longitudinal ones generally show less decline vs cross-sectional ones, suggesting that in fact older people do, to some extent, simply have lesser cognitive abilities (of the analytical sort that tend to be tested on cognitive aging tests).

I do agree that the Flynn effect can be used to reject many hypotheses (e.g. that differences between different ethnic groups have a genetic rather than environmental basis--the Flynn effect has to be environmental, so it shows that the environment can have a huge impact).

And I certainly agree that these findings can be misused.

But if IQ is strongly predictive of job prospects and the like; and IQ disparities stubbornly persist between ethnic groups; this alone is cause for sober reflection, because even the cause isn't genetic, the cause is difficult to impact.

Doesn't mean we shouldn't try. But little is accomplished by saying, "Welp, no worries, JP, we found a flaw!" We have to actually do something.

But do we know what it is?

(Aside: we're probably doing a lousy job developing the IQ of many people within each ethnic group, too. Not only the group mean is a cause for concern.)