No, he didn't say the concept of racial integration failed, he said that the welfare state failed. Forced integration has been an obvious failure, and he mentions that, mostly through affirmative action.

It is not at all true that the black middle class was destroyed by the Great Migration. I'm not even sure how that would work since the Black Middle class took steps to successfully integrate lower class southern blacks into the north. Immigrant lower class blacks did not make middle class blacks poor. I don't understand how you got to that conclusion, and it wouldn't make sense in any other environment either. The best case scenario is that the immigrant population and middle class population intentionally segregate themselves from one another. The middle class population wouldn't simply become poor.

Think of the reverse situation with selected African migrants into the US and Black ghettos. Selected African immigrants (those who are not part of a larger refugee or mass import scheme) explicitly avoid living in ghettos. The culture between the two populations is too severe for them to live next to each other regardless of complexion. Hell if we were to truly test it, \we'd see that they're different ethnic groups. We also see something similar with Rural and Middle Class blacks today. The urban cores are a ghettoizing force.

I think you're confusing the damage to black families by the welfare state with immigration from the south many decades earlier. Frankly, if southern blacks had destroyed black middle class families, the black middle class family would have been destroyed by the 30's, not the 70's. The welfare states damage is extreme and fast. Black areas were absolutely ravaged within 10 years of the Civil Rights movement, and have been continuing to be an unmitigated disaster every decade since, getting worse and worse.