It's so much more complicated than that. Sure, there's probably not much more efficient than a fully loaded A380, but airlines that doesn't present the full picture if there are connections. Also, on the same plane, longer flights are often less efficient than shorter ones because the plane needs to carry extra fuel. Further, actual seat density matters: a full A380 may be very efficient, but an empty one is miserably inefficient.

Today, airlines are so competitive, they build airplanes for specific routes. To do a proper analysis, you need to analyze a specific route, look at the competition, what they are flying, their utilization, etc.