You don't think some in the tourney couldn't benefit from having a coach the back seat giving them tips on S.A. and tactics during the fight?
By the time the back seater takes the time to verbalize what the pilot should be doing it would be too late to execute the move. Dogfights aren't fights where you can think of you options, discuss these options with your coach, and then execute the agreed upon maneuver. You have to read the situation and react to it in a nano-second. One second to late and the move is useless. I doubt the back seater could verbalize what you should do quicker than half a second to give your brain time to hear what they said, proccess it, and then act upon it.