I think the weight difference would not be so noticeable, that one car would need to brake and the other not.
Also racers have always been trying to reduce rotating mass with smaller multidisc clutches and automatic transmissions with no torque converters. Allowing better response coming out and going into turns.
http://www.autotransdesign.com/produ...0000081_th.jpg
This would be almost the same as saying a heavier car slows faster.