How exactly do you think launch control works in a way that makes it different from traction control?
Schumacher makes the best starts? He's never been known as a great starter, good at aiming his car at another off the start but not really a notorious fast starter. He might have done well in 94 and this year but previously he's not been outstanding.
Launch control also operates on the clutch and sets things like the biting point for the start, holds the car on the brakes so everything is preloaded before the lights change (in the case of Renault, for a bit, detected the jump start system switching off and so launched the car without the driver doing anything) and rate of engagement of the clutch along with throttle and ignition control.