You seem to be operating off the straw-man that I'm saying that all white kids are inherently smarter than any black kids. I'm not. I'm saying that parents who have well-below-average IQs are more likely to produce below-average-IQ kids than above average kids.
Thus the kids of multi-generational white underclass of England are likely to be of lower IQ than any kids which Thomas Sowell would produce.
The performance of adopted children belies that contention. Any population can produce very bright people with the right education, as Jamie Escalante proved.