Detroit's big problem was that their entire economy was based for 100 years on one industry. An industry which went into steep decline so that the population has collapsed as people moved to other cities to find work and many couldn't sell their homes so they simply abandoned them. Drug dealers and homeless people moved him, thieves stole everything of value, while arsonists burned down what was left.
This is what Detroit needs to do. They need to bulldoze 50% of the city. Just knock it all down, rip up the streets, remove the power lines, pull the pipes out of the ground, and turn that land into parks, open spaces, and urban farmland. The city's main problem is their trying to maintain the infrastructure of a city that is four times the size with a population and economy that is 1/4 the size and they can't afford to do it so just stop trying. Raze the outlying areas and concentrate on redeveloping what is left at the core. This will remove most of the urban blight and actually restore a viable economy (agriculture) to the previous slum areas plus the city will become more attractive for people to move to once there is lots of parkland and green open space around it.