Weight can help efficiency
I am an aerospace engineer and can give you an example of an increase in weight improving efficiency. That is the addition of winglets to an airliner. These add considerable weight from the winglets and the wing reinforcement needed to carry their load. But these winglets increase aerodynamic efficiency and decrease fuel burn by up to 7 percent, which is a huge savings in the cost of operation. Possibly adding the extra weight to the ferries has a similar effect. I don’t know but I would be careful about criticism before knowing the facts.