It's trying to prove that the cargo wasn't that heavy and the weight of the truck was high. Which leads to a false "wow" this truck can move this much and still retain miles before charging.

As with the Ford lightning real world tests prove, towing with an electrical vehicle significantly reduces your miles. I can imagine that if the Tesla semi was max cargo, their claims would have to be significantly lower than what they demonstrated.

As it stands, the E350 cargo van seems like the only sensible electric hauler. It is geared towards short sprints around town and daily charging while home though.

I'm not knocking the idea of electric and towing, but there is a ROI with packing weight into a vehicle and it's ability to get miles. Personally, I think current tech allows for a swap of battery packs or trucks to keep drivers going for the amount of hours they travel. It's not like long haul drivers can just stop and charge midway, let alone the infrastructure needed for pull through overnight charging at rest stops. Logistics and tech are currently holding back electric for long hauling, but any progress is good coupled with, having to start somewhere.