As we all know, I think prosecutors are some of the most vile people on Earth, but I don't think they intentionally seek to imprison all black people while letting the white folks off the hook. There are a ton of factors at play here, and overt racism, while certainly a real thing, isn't a very big one.
Consider that poor and minority neighborhoods are generally subject to proactive (as opposed to reactive) policing. More arrests right off the bat. Then factor in that in those neighborhoods there are more likely to be aggravating factors involved. Gang membership. Gun possession. A general (and quite reasonable, IMO) distrust of cops that could lead to a more adversarial encounter. A greater likelihood to be a repeat offender, which leads to MMS (where the for-profit prisons really hit the jackpot). Most importantly, the number of people who sit it out in county until a freshoutofcollege public defender shows up to recommend a plea bargain because they don't care, don't have the time, and don't know any better. People with means Call Saul and either fight their case and win, or take a much better deal because Mr. Scumbag DA doesn't care enough to take on a real fight.
I think the issue is more about the CJ system as a whole than the way drug laws are applied (again, excluding crack laws). People are looking at things in terms of race, and I suspect if you looked at things from the wealth perspective you'd see a much better sampling.