Vehicle mass is a significant factor in collisions between vehicles because taking two thirds of the impact is a meaningful increase over taking half of it. Heavier vehicles are much more dangerous to lighter vehicles.

It's basically irrelevant in pedestrian collisions because the pedestrian is already taking ~95% of the impact even from a lighter car and the <5% difference between that and an arbitrarily heavier vehicle is completely dwarfed by any of the other variables like the speed of the collision. For a pedestrian it's better to get hit by a freight train at 35 MPH than a 3000 pound vehicle at 39 MPH.

You think cutting the weight of the truck is going to make it safer for pedestrians?

This is the silliest argument against the Cybertruck, IMO. Its forward visibility is significantly better than other full-sized trucks, yet people continue to bring up pedestrian safety every time the Cybertruck is mentioned.