vfrpilotpb,
The disk loading is calculated by dividing the thrust by the disk area, and has units of pounds per square foot. If we add more blades, or widen the existing ones, we don't change the disk loading, we would reduce the "blade loading" of the rotor system. Believe it or not, that can cost more power, because with more blade area, we can operate at lower angle of attack for each blade, and that almost always reduces the efficiency (increases the power for a given thrust). With more blade area, the disk can produce more thrust before it stalls, but at a lower thrust, too much blade area takes more power.
The reason why more disk area takes less power is explained by that downwash formula we used when discussing VRS. A bigger disk handles more air, so the speed change on the bigger package of air can be less for a given thrust. Less speed change means less power needed.
Nick