The question is: even given the current system, are some cops "bad apples" who, if "fixed" somehow or removed from the system, would give us a considerably better outcome?

And the data says: yes, because the number of complaints is strongly skewed towards a modest fraction of repeat offenders.

Any time you get a situation where individual variation produces a large outcome, a focus on individual responsibility and character--completely aside from the group--can produce important results. It doesn't even have to come from within the police department: city councils can set up oversight committees and get the bad apples out even if the police department proves unable to do so itself. (This is not a great solution. Constant internal tension makes for difficult governance, and historically, the police departments have usually won the jockeying for influence. Nonetheless, it's quick to implement and I think if the focus had been there rather than "Defund the Police" after George Floyd, it could have been very widely implemented. There was political will to do something, but political will doesn't last long.)

My point is that yes, you're right that the group culture is very important; but that doesn't mean that individual character is not also important. One way to fix individual character is to have the right group culture, but it helps to actually keep some focus on individual accountability. You can't drop it and only focus on groups. That's my point, and it is my point because that's what the data suggests.