There is no vent to the attic. If the AC unit and duct are in the attic then it will benefit efficiency tremendously. Either way, the attic only gets heated/cooled from exchange through the ceiling.
There don't need a vent to the attic. Heating and AC will work harder without the ceiling between the attic insulated.
Which part of the AC is in the attic? If it is the compressor, then you can't insulate the roof. I have ductwork in the attic, and you just insulate the duck work.
Is your attic ceiling insulated?