Kieth I think you have the basic principles covered in that the individual car operation has evolved to a level that one person is overwhelmed by the complexity of a contemporary nitro car operation.
One manager overseeing the service of the car between round and pre race set up and preparation.
A second management personal evaluation the operation of the car, weighing track surface conditions, weather conditions, historical data of past racetrack performance combined with the potential of the current tune-up.
Now the second manager type combines the input from the first person's report, input from the historical database compensates for any changes mandated from the damage/performance evaluation from the prior run, make appropriate changes to the tune-up and/or clutch to suite the desired goals, weather that is to maintain the status quot or improve performance levels.
A change in the environmentals just from the time of day will require an adjustment in the set-up just to run the same ET. The two management types will always discuss the options, and soliciting experienced department heads opinion. In the multi car team environment the resources are enhanced by the shear volume of personal. The baseline being the same for all the team cars gives a big advantage, as the data base grows exponentially. So your .250 second drive-shaft speed numbers are easily referenced to how close to the edge you are on that given day.
So Crew Chief, Tuner, Car Chief, are Titles and historically the Crew Chief is the guy getting the biggest pay check and that's where it all stops and starts on race day.