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While I think the central point, that there hasn't been much in the way of African Americans in rock lately, I think Hannaham is playing with the boundaries of genres to make his point.
This may be the only time I have ever heard anyone refer to Living Colour as funk. There was a ton going on there, but they broke onto the scene as a hard rock band, and their second album, while somewhat overlooked, is an amazing mash up of genres. It actually did break quite a bit of new ground for many of us picking up instruments around the time, because it was so genre bending. You could mix up rock, funk, jazz, r&b and even a little bit of afro pop and get a great record.
On the other hand, Sly Stone is really a stretch as rock rather than funk (anything Larry Graham touches is funky), none of Prince's famous stuff is really rock, and Funkadelic defies easily categorization, but isn't straight up rock either.
The point stands, there isn't much black rock going on these days, but it died long before sly stone, but for a few notables.