Nigerians today have to deal with the legacy of colonialism, war, pogroms and famine. (1)
https://en.wikipedia.org/wiki/Nigerian_Civil_War
"The Nigerian Civil War (also known as the Biafran War and the Nigerian-Biafran War) ... between 500,000 and 3 million Biafran civilians died of starvation."
You stated that American blacks had to deal with the legacy of slavery that happened more than a century ago. The epicenter of modern day slavery is Africa, with Africans enslaving other Africans. In 2018, about 62% of the African population endured some from of slavery.
If immigrants from Africa do better than native blacks, it isn't due to the legacy of slavery. Jamaicans, Dominicans, and Haitians have endured the legacy of slavery too, yet these immigrants do better economically as well. If systematic racism was real, it would hold back all blacks.
They may well be right about that, and yet there's still an obvious difference there. Also, keep in mind that immigrants tend nowadays to come from the better-off strata of their home societies. There was a study about this making the rounds just recently, but I've unfortunately forgotten what it was called.
Additionally, it's important to note that modern day racism is more damaging to already marginalized groups or those that have historically suffered from it.
In other words, a well educated Nigerian immigrant may not be damaged as much by the same level of racism as a Black person decended from slaves.
There exists an underclass in Ireland who have the same origin as the other Irish - but have many of the issues that exist in the African-American community.
Live to about 50, developed a different dialect, very high crime rate - expected to be underestimated, constant violence, high domestic abuse, high illiteracy, very large families, living in squalor.
Doesn't fit neatly into any faction's magic box of solutions.
Right explains the world by Biology. The Left explains the world by Culture. The Liberals explain the wold by Environment.
It is possible that you only need to scoop from one box to find a policy - but...
If a society has not solved a problem for a long time it's likely the solution is in higher dimensions.
Our political order is good at solving problems with 1 factor or 2 factors but I think our weakness appears when we need 3 factors simultaneously because it is not possible to select for that.
See "Black rednecks and white liberals" by thomas sowell for more info (Thomas sowell is a black american economics professor and writer, for any in the audience who decide what is worth reading based on the skin color or ethnicity of the author)
No worries, people who decide who is worth reading based on skin color also introduced the oreo concept so their world view doesnt have to be challenged.
This offhand reason does not happen regularly. There are cases of places without historical slavery who perceived as poor workers and places with historical slavery who are known for their work ethics.
https://en.wikipedia.org/wiki/Nigerian_Civil_War "The Nigerian Civil War (also known as the Biafran War and the Nigerian-Biafran War) ... between 500,000 and 3 million Biafran civilians died of starvation."
This is just scratching the surface.