He found that the police were somewhat more likely to act in non-lethal interactions, and somewhat less likely to use lethal force.
That's hardly what you said - that it was inarguable fact that police are more likely to target and kill black Americans.
As for his research being criticized, so was the Cass report. In general his research was well received, and it's difficult to suggest it was biased, as it was not what he expected to find and in fact he redid it all with a new team after getting those results the first time.
Almost all research, even when it is good, gets some critical feedback on method and approach, and it's important that it does. But that does not mean that just because there is academic discussion or criticism you throw it out.
If you are going to go around telling people that there is zero question something is true and inarguable, your data needs to be totally uncontroversial and universally supported. That's clearly not the case with this subject.