The voters entrust the mayor to run the city, so it stands to reason they should trust the mayor's decision on which people get to brutalize the citizens

A pair of incompetents in that picture.

Well, under American constitutional theory, the legislative branch oversees the executive branch, and the former can investigate the latter at any time. (Why Seattle needs a special law to enable the investigative arm of the Council to investigate the Police Chief might be a better question.)

If the Council had wanted to know what happened during June 2020, then the Chair of the Public Safety Committee should have had that Committee issue subpoenas to the Chief of Police, and to anyone else who had relevant information. Instead, CM Herbold wasted everyone's time with this garbage: https://www.thestranger.com/slog/2020/06/30/44008034/we-must-end-the-conditions-in-chop-that-are-leading-to-violence-and-death

"That measure would prevent law enforcement officials from playing a farcical game of hot potato like the one they're currently playing over Durkan's and Best’s deleted text messages."

No, it wouldn't, because the City can't compel King County or Washington State to do anything. All the bill would do is direct the OIG (the Council's investigative arm) to consult with its counterpart at the state level. There's nothing to prevent the state from bouncing the request around, or back.

(Oh, and the Stranger really, really needs to stop pretending anyone else cares about those deleted text messages. Just let it go, already.)

@1: What brutalization? Do tell!