Other than for social or ceremonial purposes I think there's limited benefit in trying to equate Police and military ranks given that they gain their authority from very different sources.
As for commissioning from the ranks I tended to find that the often quoted empathy for lower ranks etc was a very perishable trait.
It was always the police ethos of course, that everyone came from 'the ranks' this was viewed at essential because everyone, regardless of rank, is first and foremost the Queens Constable and they should know what that means and how to use that authority. The latest idea that people can be 'parachuted' in at a higher rank flies in the face of this.
A cynic may surmise that this is more about eroding the culture of policing that improving leadership.
There's a tendency to believe that Policing can be run like a business with measured inputs and outcomes and staff who can go from job to job as though on a production line. That's not the case. Policing is a job with a range of tasks as wide as all humanity can think of. An officer can in one shift go from chasing noisy kids out of a park to taking a Burglary report to giving first aid to a stabbed and dying teenager. If that seems fanciful to anyone it's not. I did it on 3rd May 2007 and it remains with me to this day. You don't just clock out from days like that. I struggle to see how many coming from an outside industry will get that.