I suspect when it comes to the existence of black punk bands like Death and black rock bands and musicians in general, they often feel like the real thing. There are black people, even some Africans who like listening to rock music and there’s a Goth scene in Kenya and a metal scene in Botswana. So rock music does exist in Africa.
Actually if you want a stretch, black guitarists (irrespective of genre) do exist. You’ve got Cameroon’s Kareyce Fotso who did a number of delightful songs. Then there’s Tinariwen, an all-Tuareg band. Those are some that I could name but they do deserve a mention. It seems parsimonious to say that they often get ignored in favour of their white counterparts.
It’s not that Clash necessarily did cultural appropriation but that those bands are not being given enough credit. Let alone any focus outside of their relation to white musicians that they’re worth listening to and given a damn about.