Doctors have their own personal liability insurance, if they make too many mistakes they literally cannot afford to continue working in medicine (or have to move to a lower risk sub-field that have lower base premiums).
If police held their own individual liability insurance, and it too could become uneconomical for them to continue to practice law enforcement, I'd consider that a huge improvement over the status quo.
If you want law enforcement to be comparable to medicine, then oversight is going to raise tenfold.