No, you’re missing the point. It’s not about the emergency vehicle itself hitting pedestrians. It’s about the fact that having a very large vehicle, such as a ladder firetruck, as the “design vehicle” for the street forces engineers to design in a larger intersection turning radius, which increases regular cars’ speed through the intersection. That is what decreases pedestrian safety.

See also: https://nacto.org/publication/urban-street-design-guide/design-controls/design-vehicle/