However, Detroit was ~30% white in 1980, 3x what it is today, and untested rape kits surely fed a perception of intractable crime over the intervening years as white flight killed the city.
Check it out at the Dot Project (turn on the overlay in the lower left).
https://demographics.virginia.edu/DotMap/index.html
That line between green and blue between Warren and Detroit is 8 Mile Road, and yes the split between the south and north sides really is that stark.
Wayne County extends west to Livonia and Plymouth, which is a white, affluent, low-crime area. And south through a lot of other white suburbs.
It's completely believable to me that a random, non-discriminatory processing of rape kits would result in 86% of untested kits coming from people of color on that map.
You have to look west and south of detroit to see wayne county that isn't detroit
While you're couching this as hypothetical - this is in direct contradiction to what the prosecutor said as well as her experiences.