Edit: I misunderstood what OP meant by trucks. NVM
How are light weight vehicles more efficient than trucks? That’s such a broad statement with absolutely no data provided to back it up. Efficiency matters a lot depending on the context. Delivering 40,000 kg of good cross country? Even a diesel truck is going to be more efficient than 10k little robot. Last mile delivery? Yes, obviously it’s not good to send a semi trailer to deliver a pizza.
The point is, those big fat trucks aren’t just there to annoy you, they are doing something pretty useful.