It's about many things, including reaction speed, visual awareness, specific expertise and informed decision making wrt braking or acceleration power. All of these are better in a modern self-driving car (I do not know whether Tesla falls into this category) than in a human.
https://waymo.com/safety/impact/
Over a given driving distance, compared to humans, Waymos produce a 90% reduction in serious injury, 90% reduction in pedestrian strikes, 83% reduction in airbag deployments, 85% reduction in cyclist strikes.