Detroit had a black mayor by 1974 when it was still well over 1 million people and still a viable city. I'm not sure what the racial makeup of the council was.
We go back to the city income tax when many cities have a city income tax. In fact, over 20 cities alone in Michigan have an income tax. Detroit is pretty low tax, relatively speaking, among most major cities. The black middle class you mentioned even left for whiter pastures when they started moving to Southfield and Oak Park.