That depends on the design as well. A flat "sports"/sedan style car just levers a pedestrian with the hood - the legs will be broken, yes, but in most cases the pedestrian survives. A SUV or particularly American "truck" style cars in contrast just smashes the pedestrian's whole body to a pulp - see e.g. [1] for a visual.
On top of that, modern cars have a ton of automated systems doing stuff like pedestrian detection visually indicating pedestrians and bicyclists in the dead spot(s) and automated brake assistants, not to mention ABS/ESP assisting the driver in emergency braking to not lose control. An old car does not have these features and thus has a higher chance of the driver injuring others on the road.
> and a sedan getting plowed into by a truck, modern and huge, or old and huge, is still just getting plowed into by a truck.
A modern car/SUV absorbs a significant portion of the crash energy in its own body, additionally so does the other vehicle. An old car does not.
[1] https://smartgrowthamerica.org/bigger-vehicles-are-directly-...