Comment by kn0where

Yes, weight alone is not that important for fuel economy at highway speeds. Aerodynamic efficiency of a vehicle is determined by the cross section area + drag coefficient. A 90s Honda Civic has a worse drag coefficient but a vastly smaller cross section than the Rivian, so it needs to move less air out of the way to drive forward. Smaller EVs can go farther with smaller batteries, but the American consumer has decided for one reason or another that cars must be tall, and therefore less aerodynamically efficient.