Naturally this effect cancels out if all competitors get the same visual cue, however it's still to the benefit of athletes and fans to want quicker reaction times:
- Shorter overall reaction times means faster races means better records
- The standard deviation of reaction times is smaller for sound than for sight, which means the reaction time is more fair to all
The auditory system, on the other hand, is optimized for speed. It has a giant synapse (=connections between cells), called the Calyx of Held, that is specialized for extremely fast (sub-millisecond), reliable transmission between cells. They're really cool looking: https://www.eurekalert.org/multimedia/pub/213595.php?from=44...
I did note at the time that the gunshot sound put an extra oomph into the start over a buzzer. No idea whether that actually made a difference to my time, but it sure got my heart rate up.