"Heavier vehicles always do better" You are wrong. At least in the perspective of crash tests. In a crash test against a wall (equal amount of kinetic energy

"Heavier vehicles always do better" You are wrong. At least in the perspective of crash tests. In a crash test against a wall (equal amount of kinetic energy transferred to the wall and to the vehicle), a lightweight vehicle does better than an otherwise identical but heavier vehicle. This is because its mass is less, therefore there is less kinetic energy to dissipate. However in road crashes, heavy vehicles fare better because the heavy vehicle transfers more kinetic energy to the more lightweight vehicle. NHTSA crash ratings are well known to not reflect this difference. But the point remain that heavy vehicles are disadvantaged compared to lightweight vehicle, and the fact the Model S does so well despite its weight is a testament to its good crash resistance.