They don’t have to lose full control. They could be following too closely and swerve onto the sidewalk to avoid a collision with a car and end up striking a pedestrian.

This is a matter of the human factor - and you can never make that disappear. There will always be the odd idiot driver.

The reduced speed limit should also be accompanied by lane narrowing, speed humps, and other traffic calming techniques.

This is totally fine for housing areas, but definitely not for through-roads. There’s no one-for-all solution in the same way our bodies don’t have only one size of blood vessel.