I haven't watched any of Spike's films in the recent past but to my recollection, his characters usually aren't deeply drawn. And this movie is no exception in that sense.

Like you said, you get no sense of the man Ron is and even less of the other characters, except maybe Flip, who probably gave one of the best moments in the movie when he outlined his relationship with his heritage.

Also, do we really accept that Ron's partners would be so gung-ho with a rookie jumping the line and leading an operation? And one so potentially dangerous to Flip? And while there was a couple of cops who used offensive slang while Ron was in the Records Room, isn't it clear that a police department would have more than one racist? Granted, doing all of that justice would have taken a mini-series to flesh out. But I think people who don't like the movie are right to think the movie's characterizations and writing wasn't up to par with the emotive qualities the movie did so well.

Also, Ron's internal conflict was rarely addressed on screen. Like I get that he wants to make a name for himself and exposing the Klan was an extension of the radicalization he had after hearing Ture speak. But you can't tell me that spewing all of that racist rhetoric to Duke, Walter, and the other Klansmen didn't take some type of psychological toll on Ron or the fact that he was an embodiment of the 'double consciousness' that was only hinted at during the scene with the BCA President in the park.

Spike was obviously less interested in describing the interior life of Ron than showing him as a hero. But hero stories are usually more impactful when we see more of the internal obstacles at play.