All other things being equal, that's true. All other things are not equal though. The 4000lb+ vehicles often have worse visibility, so you have to pay more attention to make sure a kid didn't wander in front of your truck while you were waiting to make a right turn.

>A distracted driver can kill pedestrians just as easily in a 3999lb vehicle.

No they can't - a lighter vehicle has a slightly harder time killing people. It's still incredibly easy, but the pedestrian fatality rates do go down the lighter the vehicle is.

Haven't we proven that the sense of invulnerability leads to worse outcomes as well?