Sure, but part of the point of in-effect racist zoning policies is that the affected population is predominately the targeted minority. It would be more effective and more equitable to address the actual issues created by flophouses.

Single-family zoned areas by definition only have single-family homes, and only some families will be able to afford those homes. The designers of such policies are often well-aware that the only families affluent enough to purchase or rent a home in such an area is of the preferred race (thanks to the strong racial correlation to socioeconomic class, as well as historic explicit racist policies like redlining, employment and education segregation, etc etc).

To be clear, I don't believe that single-family zoning is necessarily racist, especially with the continued democratization of the middle class. Single-family zoning is bad for a lot of reasons. Its just that it is absolutely the case that historically single family zoning was deliberately used in several cases as a racist policy, but in such a way that it would pass muster in court.