The 747 takes only about 50% more passengers in most seating configurations. However, that does not make it cheaper or more efficient to operate because it's harder to fill the plane especially when flying from smaller airports.

Meanwhile many 747s are only in service now because fuel prices are relatively low. Once the prices go up they will likely be replaced by 777s or other models that are easier to fill up and cost less to operated.

I confirmed this recently with a United Airlines 747 trainer who was booked on the same 747 flight as I was. He loved the plane and didn't want to fly anything else.

I'm pretty sure the metric has been a little distorted by the improved sardine packing.