A spin masters absolutely nothing they are a basic and boring maneuver that in any trainer aircraft is nothing more than throwing full rudder full back pressure and when you want to get out of the maneuver you can release the controls and within a half a turn you are recovered.
You're right that a spin does nothing for teaching coordinated flight. That isn't the purpose.
Coordinated flight is a very basic skill that should be comfortably mastered before beginning spin training. The main purpose is to overcome the psychological fear of the airplane.
You can practice the rote maneuvers of Chandelles and Lazy 8's and get so good that the ball looks painted in there, and still lose it when a sudden upset throws you over 90 degrees and your heart stops and you ....
Overcoming the fear is the only good reason to teach spins to pilots. How much the fear/freeze factor contributes to accidents, we cannot measure.
That's why the influence of spin training cannot be measured.
The fact that all of our modern (post 1950) airplanes are pretty spin resistant is the reason it seems over the top to train spins, and the government has taken them out of required training,....and our government sure knows what it is doing, doesn't it? ..but stall/spins keep happening. Pilots freeze up when they encounter all these other factors that everyone talks about; weather, pax pressure, new machine/environment, etc. These are the things that can be seen and measured. The pilot's personal fear factor cannot.
I see spin training similar to actual IMC training....gets you over that initial fear factor.
On the subject of "legal ain't safe"... What has gone missing in our society and legality is the concept of morality in judgement. The current crop of "legal" financial moves done by Wall Street and Our Government
have caused a melt down of the system. Their cry is "We didn't do anything illegal." But they knew they were robbing us.
A professional includes morality in his or her judgement of "legal".
Even if you have 5 hours in the Beech 18 but don't feel safe in it, you are not legal. That's a professional opinion. I know that their are many people who consider themselves professional who will argue with that statement, and I would lose in our current court system where professional morality has already been lost...but there are some 'old school' judges who will still agree with me.