I think the important point is that self driving cars are likely better than the averaged real world population of existing human drivers at avoiding pedestrians.
It matters who is driving what cars. If you're taking safe drivers and having them drive FSD cars, and comparing the average of that against the average of all non-FSD driven cars (which includes a lot of really shitty drivers in the average), then the net safety impact of this could be nothing. Introducing FSD cars would have no impact to overall car safety, and might even have a negative impact, if the FSD software is worse than the good drivers who are now not driving manually-steered cars but are driving FSD cars instead.