Well they aren't going to come and work for you unless you pay them more than what they're currently being paid (unless they're moving for something like life reasons) so I don't think there is any more relevant number than that.

Of course it's relevant - it helps them understand what can tempt an employee away from their current job. That's why it's worth hiding it. This law stops it being hidden.

You think it's an advantage to companies to post more accurate pay bands - right? You said "It will be obvious that if a labor buyer is putting out $min wage to $1B pay ranges, that they should be ignored and/or they will get the worst applicants."

But they can post narrow bands right now if they want to - they don't need to wait for the law to tell them do it.

If it's an advantage to them, then why aren't they doing it anyway?

I would guess that the answer is it's not an advantage, because most of the time their pay is bad, and telling people up front does not help them. I've seen this with companies like ThoughtBot and GitLab that make a big deal out of pay transparency... problem is they're being transparent about how bad their pay is.