I don’t know enough about physics or cars to really rebut you but this doesn’t seem plausible to me.
I don’t think aerodynamics are particularly relevant to towing? Prime movers (tractor trailers?) are about the least aerodynamic vehicle there is but they regularly tow more than 100 tonnes at highway speed.
If I had to guess I’d suggest the primary problem is the relationship between system weight of the vehicle and load, battery capacity, and the battery’s weight. As in, if you want to be able to cart 1 ton for 200km then the additional battery requirement is another 300kg so that’s really only an extra 700kg so you need more battery and heavier frame and so on.
Another problem I suppose, and I emphasize that this is supposition, is optimising motors for both torque and speed. The torque required to break inertia with lots of weight in sandy or muddy terrain.