The arrest/conviction generally follow the pulled over stopped rates. It's pretty hard to arrest/convict people you aren't stopping. These types of biases and stereo types are often pervasive within certain groups of people, including law enforcement, prosecutors, judges, and often the subset of the local community in power. If you've ever been to court (even traffic court) you'll find the word of the officer is given tremendous weight, while the word of the defendant is almost totally marginalized (no matter what your race). Even though you are "presumed innocent", the defendant has a natural incentive to lie and the officer presumably doesn't.

To top that off there is almost no "suitable oversight" of any police departments in the US of any kind, let alone by the community.

There really are no simple solutions to this, even places not plagued by bigotry and racism have major structural power problems for the average citizen.

I didn't say this was a solution or that the problem has a simple solution, but pretty much any solution needs to start with community involvement and community oversight seems a useful component to consider.