Well the speed is the speed of light, ideally this should have low latency. The datarate will be effected by how quickly you can turn on and off the light and that will have some limits.
Latency in WiFi comes from interference and contention (wait until other devices have finished sending; this has improved with Wifi6 AFAIK), and some other, probably less significant factors. Travel time of the signal through air should be the same.
Light and radio waves are the same physical phenomenon. The difference is the frequency. Light is much much higher frequency than radio. Nuclear radiation are even higher frequency. Maximum throughput with maximum damage!
