I was informed by a figure in the Irish mob of Chicago, that the reason C-town works is that a) the Mayor is a benevolent dictator and b) no one group in the city is big enough to dictate outcomes so the Mayor needs to cobble together coalitions to get anything done. This allows for horse trading, etc.
Detroit meanwhile has the dictatorial mayor but he's got no effective opposition and the city council members don't represent specific geographical areas of the city but serve 'at large' so whole swaths of the city just go to seed....
Chicago is broken down according to: Irish, Italians, Polish, Hispanic and Blacks. Detroit is just mostly Black.