What he’s saying is that he agrees with you- for higher loads, two motors better than one.
Conversely at low loads one motor is better
For long range, what do you want to be at, low loads low speed or multiple motors at a higher speed (peak efficiency on the power band)
Only problem with that is wind force (basically dominating your losses) increases with the square of velocity so you really need to go low and slow for a max range and then one motor works better
Better way to put it: you will gain efficiency with multiple motors as you go faster. But for each mph the wind force will eat your efficiency gains several times over