[candiodari]

The TLDR is, on the surface of the earth the slower you're going, the more efficient it tends to be. That even holds for, for example, making trains or cars move slowly: they'll be most efficient at a pretty slow speed. Even planes are most efficient flying 0.0001% above stall speed, the slowest they can possibly go.

Most energy in transport goes into moving the atmosphere out of the way.

Planes fly high, but that really only makes them comparable to a car. Surprisingly that also means that for really long-range transports even rockets aren't as inefficient as you'd initially think.