If the police get to decide the crime being committed, and the police are biased, and the police are the ones who ultimately write the reports that were evaluated for the study, how would the study detect that bias?
It really does not follow to come to a conclusion that police use excessive non-violent force against blacks, but not excessive violent force. Sure, it's possible.
But then, consider: in the past few years we have been presented with videos of officers shooting unarmed blacks, in which the blacks would have been found at fault had it not been for the video evidence. Samuel DuBose and Walter Scott, for instance. How many unarmed suspects have been "upgraded" to armed and dangerous suspects? As long as you're killing (and framing) them in the right ratios, it doesn't matter if they were actually guilty of something?
Are DuBose and Scott rare cases? We hope so, but we do not know without bodycams, and with bodycams cops and suspects alike exhibit better behavior (so we may never know). At present, I don't see how anyone can say "Clearly, blacks are not being wrongly killed."
As for cops vs blacks and blacks vs blacks, I see no reason why we can't strive to improve both situations.