Can't quote law but IIRC cops have pretty broad powers to do stuff "for public safety" if they deem it necessary or just a "good idea", and that would include stuff like seizing weapons in a crowded situation where violence was common.
I think that is why signs at political events and protests are always put on soft cardboard tubes, and why you don't see people carrying swords and axes at those events, or guns.
What is "brandishing"? Is that holding gun is "firing position"(pretty much anything but slung on back)?
Yes, there is a big and scary (and non-Constitutional) group of "police powers" that can be enacted for "public safety", and are ripe for mis-use.
When the cops shut down a road (supposedly due to snow) and order all cars to drive somewhere, they don't need any court order to basically put you under their total control.
Decades ago there was some "Road House" type nightclub that opened somewhere in the valley around Bakersfield. Story was owner didn't make the expected donations to Police Benevolent Fund, and strangely for a few weekend nights in a row of his "grand opening" the local cops found reason to block the road leading to his fairly isolated establishment....so he fairly quickly and quietly went broke. There aren't any hard and fast regs on what allows the cops to close a road to traffic, or how long it takes to clear a fender bender or crate of spilled tomatoes.