I don't understand your question here.
> how would you fix eg. the corruption of power, causing police men to overstep?
The same way as for everyone else, with incentives based on post-facto enforcement. There's no justification for police to escape being bound by our laws.
You prosecute them personally for say 2nd degree murder, getting rid of "qualified immunity" or other entity liability shield. My point is precisely that the system currently lacks this justice (eg George Floyd's murderers being prosecuted was an unlikely event), and you can't rely on just training cops to be "less bad".
For lesser offenses, there would need to be a finding whether their actions were congruent with written department policy (in which case the department would be on the hook for damages and/or criminal conspiracy), or whether they were not (in which case they would be individual perps as above). But this liability should extend all the way to wrongful arrest/imprisonment, righting corruption like "you can beat the rap but you can't beat the ride" and other externalities that have become routine.
