I was once convinced and indoctrinated by Sowell's eloquent writings and powerful speeches. No More.
Culture, while important is not the ultimate determination of success for either individuals or nations.
China was a socialist/communist state yet it still outpaced many other third world countries, even free market nations including those in Africa and Latin america. This was before chinas own market reforms.
N korea was 100% command economy, but it still has the capital and knowledge base to produce nuclear weapons and modern rocket technology.
The economic system, while significant, it is not the ultimate factor in a nation's level of achievement. Control for variation in economic systems, and you will find that the quality of human capital will make all the difference regardless of culture or even education levels.
The secrets of genetic based intelligence are no longer 20 years away. They are no longer a result indirect evidence (twin studies). The power to unlock genes for intelligence is a matter of 2 years or even months away, and significant/ direct links have been found recently.
It's over for Sowell's theories just as it's over for all of the modern progressive theories.
It's time to embrace a controlled meritocracy with a market-based micro-economy and controlled macro economy similar to Singapore or China. This is the only way forward.