(1) Systematic racism doesn’t mean that members of certain groups are entirely prevented from succeeding. It means that they have a harder time succeeding than similarly situated members of other groups.
(2) Various researchers have found that the nation of origin matters. The biggest factor is the availability of education, and immigrants from sub-Saharan African countries tend to be better educated than both immigrants from European countries and native-born Americans.
(3) When we compare black Americans who immigrated to the US to black Americans born in the US, those with similar educational outcomes tend to have similar levels of achievement. So the relative success of African immigrants comes, at least in part, from the selectivity of the immigration system.
(4) And since education is such a big factor here, it is worth noting that racism affects educational outcomes. To the extent that African immigrants may not have experienced the same racial stressors during their formative years (depending on their country of origin, of course), they may have an advantage (though that advantage may disappear once they immigrate).
African immigrants may be successful as a group, but that is at least in part because those whose applications for immigration are approved are already more primed for success than similarly situated immigrants from other countries. When the data says that members of certain groups have to be twice as good to achieve half as much (or even just better than average to achieve average results), we haven’t found evidence against the existence of systemic racism. We have found evidence for it.