Spinning in low gear uses the human body's capabilities more efficiently. Whether more or less distance is spun is less important because it is so much easier to pedal low gear/high cadence. It's the difference between jogging and sprinting. High cadence/low gear keeps it a mainly cardiorespiratory endeavor while low cadence/high gear is just your quads vs your ability to suffer. You can look at the legs of distance (tour de France) vs sprint (track) cyclists to see the difference in body composition from each approach. I'm not arguing with your reasoning. I've only ever measured watts not watt/hours.