It seems to me you are confusing points. First is Kap: is his view legitimate or not? I argue it is not because it is a blanket treatment of cops as bad. This is not shocking; he is not alone in this view - saw very similar views just today in my liberal community arguing that police should not be called for altercations because they just shoot all blacks dead. That's what they do because they are racists. So is his reaction appropriate? Is this general reaction to police appropriate? Is Kap reacting in the right way? Well, considering people in the NFL want nothing to do with him suggests that he's reacting in an inflammatory way. Kap's reaction is the main issue, because as I said, police encounters happen by the hundreds of thousands and Kap is making like these highly charged and publicized cases that show police in a bad light are the norm, and are certainly due to the pervasive racism of police. A lot of people don't agree with him, even those who strongly believe there is a problem.
Second is whether the cop is a murderer or manslaughter. Possibly, but the jury didn't agree. More likely, as you point out, he's a poor police officer, who doesn't have a good sense of whether a situation is escalating to a confrontation with a 'suspect' or is just a situation with a guy who is high and impaired, has a gun, but is not a threat. The police force will determine that. I hope they have enough motivation to remove a bad officer over protecting 'one of their own.' If scrutiny could do anything it might make police more carful about techniques, training and evaluation. But again, there will be mistakes and difficult encounters even with highly trained and decent officers. The actual result of much of the recent scrutiny has been for police to withdraw from positive policing in communities, and in many cases, it's led to more crime.
If the press decides to continue their protocol of advancing the narrative that both incites and confirms anti-police bias, you'll continue to see the very rare cases endlessly running on video loops, so long as they can get the video. There are plenty of resources to find out the exact level of police bias but I suspect our essentially leftwing media and entertainment industries will continue to sell the story of rampant institutional police hatred of, bigotry towards, and indiscriminate slaughter of racial minorities. It looks like for now, the NFL and fans aren't buying this extreme view. If Kap wants a job, he's going to have to moderate his tone or vastly improve his game to become indispensable.