Who defeated the first iteration of the KKK? It wasn't local sheriffs, it was the feds.
Who brought charges against Ahmaud Arbery's killers? The local PD cleared those lynchers. It needed the Georgia state authorities' involvement.
Local police authorities can be of highly variable quality, and they don't have as much oversight as the higher levels of law enforcement. I'm not inclined to trust in them more just because they're "local". Their closeness often leads to massive conflicts of interest. Trust has to be earned.
Regardless, one isolated example is not evidence of anything. Everyone agrees something very wrong happened in Uvalde.