You have this exactly backwards.
It's telling that instead of mentioning doing away with warrior training, for instance, you list things we, the people, need to do to deal with poorly trained cops with licenses to kill, which, in the case of the police, is exactly what this immunity grants.
The police need better training to handle the people they serve and protect, period. The police need to perform better psychological evaluations of prospective cops. The police need to develop better community relations with the communities they serve.
I agree with reforming the unions and installing more independent civilian oversight. I also agree that the U.S. needs major reform of metal health and drug rehab, but that particular issue is more of a left outer join with the issue being discussed; they overlap unfortunately, but the all-too-often grim outcomes of that overlap are due to the state of policing.
The police and their unions acting in bad faith, and abusing their immunity, is why we're here. WE don't need to clean up our interactions with police. It's the other way around.
Edited: typo, wording, and removed unnecessary emphasis