Black African immigrants (to the USA) and American-born blacks H-A-T-E each other. Aside from South African black-immigrants, I can assure you that black African-immigrants consider whites less racist against them than (multi-generational) African-Americans are. I'm not proud of the growing anti-immigrant views among Americans but (multi-generational) blacks are the worst.
If we are speaking in generalities, and it sounds like we are, then anecdotally I have witnessed similar findings that you are describing. I have seen American blacks treat Haitians and blacks from other countries with disdain, and I've seen blacks very upset about an increasing Asian and Hispanic population that are gentrifying neighborhoods that historically were almost entirely black-owned. Many black Africans view African-Americans with contempt for being disrespectful, and I've seen African-American's feeling superior because they were part of the slave trade which places them in a league of their own. I've witnessed all of that.
BUT, in the spirit of the OP on being objective, I've also seen the inverse to be true as well. I've seen white Americans being very receptive towards immigrants and I've seen others despising the idea. Take it all with a grain of salt, judge on a case-by-case basis and remember that painting with a fine tip produces greater accuracy than painting with a large brush.
"Reason obeys itself; and ignorance submits to whatever is dictated to it" -- Thomas Paine