Never is a strong word, though it's pretty close: http://jimfishertruecrime.blogspot.com/2012/01/police-involv... (not a great looking source, but obviously this is not a topic authorities like talking about). In general, I agree with all your points, and I favor a system were non-LEOs investigate LEOs.
If anything, they get to take paid time off until they are cleared of wrongdoing.
There are no citizen review boards with teeth. There is no way that police departments can self-regulate.