IMHO a lot of the inherent inefficiency in transportation has its origin in psychology, learned inadequacy, and advertising.

Before WW2 cars were sized and fitted with an engine with a sense of proportion for what their role was. Cars were simple with engines that were often under 50 HP. Even heavy trucks had small engines. Load capacity was maintained by gearing. Trucks moved somewhat more slowly.

After WW2 came the 'muscle cars' and vehicles as symbols. Most 4WD vehicles will only go off road if they back over a flower bed. IMO, while some trucks and SUVs have their capability fully utilized most don't. I look around and the majority don't often carry much more than a sack of groceries.

I don't know about penis size. I don't have any desire to have folks drop trou so a they can be measured. Or even read about it. That said a whole lot of guys do seem to be compensating for something.

Vehicles sized for the role they fulfill would be a good step forward.

As mentioned there are good diesel vehicles available. Those Mercedes models are nice ... and pricey. IMHO there aren't many appropriate and efficient diesel vehicles available at reasonable prices. Perhaps in a few years the high dollar models will show up on the second-hand market at reasonable prices. This is the real test of longevity and value.