As others have said, once you lose institutional control, and the mayor and the police chief have both effective said that they have lost this, than small reform don't matter.
Plus Minneapolis PD has a strong reputation as one of the most corruption in the nation.
https://www.startribune.com/minnesota-police-officers-convic...
https://www.patrickburnslaw.com/Articles/Business-Law-Articl...
TL;DR When a cop is fired there are several safety nets that can reinstate them. If I remember right, the union reinstates ~45% of fired officers. Neither the Chief nor the mayor have the LEGAL power to even fire bad actors in the police department. They literally cannot do anything about the problem within the law.
This does not mean that other things should not also be done.
I beleive getting rid of / modifing the police unions would be beneficial. Fixing the whole qualified immunity issue would also be good. But I also think police need representatives to protect them from false accusations or from being railroaded. Maybe that is from a union or maybe its from something else.