If we are ruling it out on the first few trips, then we are probably ruling it out for at least a decade or probably longer. I would bet the Earth version of this truck isn't going to go a decade plus without being redesigned by Tesla.
All your points about the benefits of an electric vehicle apply just as well to something lighter that is specifically and only designed for travel to and on Mars.
What? What makes you say that? SpaceX literally shot Elon Musk's car into space to do nothing but float towards Mars. The entire point is prove that their rockets can shoot something that weighs a metric ton out to Mars safely. They don't want to send something lighter that's only designed for travel to and on Mars. They want to send something from Earth to Mars that proves they can send out the materials and supplies to colonize the planet quickly.
All your points about the benefits of an electric vehicle apply just as well to something lighter that is specifically and only designed for travel to and on Mars.