The Ainu barely exist anymore, and the whole thing about the Burakumin is that they aren't visible and all their descendants hide any connection. A better example would be the Korean descendant population, but that's still a tiny fraction of the population. (I think 1 million out of 130 million or <1%?) So there's no good comparison in Japan to the ~17% African-American population.

There are hardly any pure Ainu anymore and they did not rebel against Japanese culture when they were discriminated against. Burakumin is more of a "They work in the wrong business" discrimination and is not based on skin color or a look. Burakumin tend to be Japanese in the Japanese culture and are not really outsiders.