I am actually of the opion that the Drag-profile is incorrect, as well. Deceleration in level flight is slow. The original manual indeed states to fly final approach in idle power. (It does not say, don’t make your final approach too long or your engine will stall during a go around, but that’s another issue.)
However it also says that should you make a shallower power on approach, suddenly taking away the power will make the aircraft rapidly lose speed! But that’s not what happens.