I really like the Venn diagram approach to this whole question. Any particular person’s/family’s/community’s culture is a mishmash of different overlapping factors that quickly creates thousands or millions of distinct variants. At some point drilling down too deep into the minutiae becomes counterproductive, but backing up a bit can let broader patterns that might be more useful come to light.
The Venn diagram approach also poses an interesting question. If there is a distinct “Black American Culture” and a distinct “White American Culture”, which it sounds like most people agree that there are, does that mean there must also be a distinct upper level category of “Black Culture” “White Culture” and “American Culture”? I agree that there’s an overarching “American Culture” but I’m still not sure about the other two. So we’re back to the original question. Maybe “Black Culture” and “White Culture” aren’t high-level categories in the Venn diagram but they’re instead subsets that only exist within the broader “American Culture” or “South African Culture” or “English Culture” etc. So it’s flip-flopped essentially. I haven’t thought that all the way through but food for thought.
Another point that helps give me some clarity when thinking about all this is the idea that what many white people (specifically in the US, and most likely also racist white people) think of “Black Culture” is actually “Thug Culture”. Clearly gangsta rapper types do not represent all black people, and thug types include (to greater and lesser degrees) Italian mafiosos, British chavs, and Russian gopniks. I forget who first posed that comparison, but I do find it compelling. Yes there is a lot of overlap with “Black American Culture”, but it’s not exclusive by any means. Also, which particular feature is the overarching one and which is the subset?