Use of long-haul economy

What is the use of an Economy class on long-haul aircraft?

Airbus 340-500 can fly something like, 16 400 km in 18 hours.

Boeing 777-200LR is supposed to fly 17 400 km in 19 hours.

Does anyone want to sit 18-19 hours in 32 inches?

And there are economic considerations.

The long-range planes have rather limited payloads. They have to spend a lot of fuel early in the flight to carry the fuel needed for the final approach. Therefore, they are very expensive per unit payload.

By comparison, planes that make a fuel stop in the middle spend very much less fuel in total (do not carry the fuel too far) and therefore it is much cheaper to carry people, cargo or any other payload with an intermediate stop by planes like various Airbus 330, Boeing 747 and Airbus 380.

And passengers find stretching their legs on fuel stops helpful.

Do people buy economy seats on long trips, meaning 18-19 hours nonstop while economy seats with stopover is much cheaper and more tolerable?

If not, what is the use of Economy – could it be sensibble to have no economy seats, fill the plane with premium seats, which are more tolerable for 18-19 hours, thereby decreasing payload (premium seats individually weigh more than economy seats, but take up more area, so I think there is less weight in the same space… people have roughly equal weight in differeent classes) and saving the fuel for the final extension of the range?

Is it done or going to be done in the next few years?