moving fairlead and easing the sheet
wouldn't cause the same effect as a barberhauler. Think of it this way, the sheets can have two vectors of pull on the clew, either vertical or horizontal. The fairlead controls the vertical vector by moving the car fore and aft but, the track is fixed and can't be moved port or starboard so a barberhauler is used to adjust the horizontal vector. Yes, easing the sheet would tend to vector outboard but in the doing, sail pocket would increase and that isn't wanted.
wouldn't cause the same effect as a barberhauler. Think of it this way, the sheets can have two vectors of pull on the clew, either vertical or horizontal. The fairlead controls the vertical vector by moving the car fore and aft but, the track is fixed and can't be moved port or starboard so a barberhauler is used to adjust the horizontal vector. Yes, easing the sheet would tend to vector outboard but in the doing, sail pocket would increase and that isn't wanted.