It should be said that the overall efficiency of airplanes is also terrible. It's just that there's no drop-in replacement, and therefore people are looking at e-fuels for planes. But this doesn't change a simple fact: This is very inefficient and won't be cheap.
For the curious: Boeing 747-400: 3.1 litres / passenger 100km, or 91 passenger miles per US gallon.
Better than ICE car with 1 person in it, and modern planes do better. It turns out the lower temperatures at 10km above sea level helps both the Carnot efficiency and drag. But the 747-400 travels just under the speed of sound, which hurts. Slower airplanes (but still faster than any land based transport), get you a 2 or 3 fold improvement.
