Two balls are dropped from the top of a building, one is heavier the other one is lighter, they hit the ground at exactly the same time. If you change the shape of one ball so it has more frontal area, thus more drag, it will take longer to reach the bottom. Therefore, gravitational acceleration is independent of mass. If a heavier rider and a light rider can have the same coefficient of drag, they will descent at the same speed.

Edit: until one reaches terminal velocity first, which is the light rider.