That's the point that Jim was making. In F1C they're limited to 2.5cc and something on the order of a 10 second engine run to get the model (a glider) as high as possible. Those engines are some of the most highly developed in the world and make huge HP but to translate that HP into the maximum possible thrust they can't use a direct drive because the prop needed would be far too small. Hence the gearing. A similar engine in a CL speed model would use a small (about 3" in blade length) single bladed prop on direct drive because (obviously ) they want the revs for maximum speed.

These engines are different to car engines because they're making max HP at those 30-40K revs where a car engine is way past its peak HP at full revs.