Think of it this way: Alternator x meters from load. You have a choice. The power is transported from alternator to load either on two wires (DC, rectifiers on alternator) or three wires (3ph AC, rectifier at load). Power lost is proportional to Irms^2 * wire resistance. What are the currents in the two or three wires? What does this say about wire sizing?
Since the regulator compensates for Ohmic drops along the wires, other than overheating the wires, what do the drops matter in either method?