Sitting here at lunch.
So to make sure I have my ducks in a row.
A decrease in drag is an increase in something, just don't know what.
Example air is fluid so to not disturb the fluid and keep it laminar you would need a 23mm wide rim for a 23mm wide tire with 32 bladed spokes to keep the rotating surface mostly disc shaped. Thus keeping the fluid mostly undisturbed. Resulting in a decrease of drag. This only comes into play at speed greater than 15mph.

Reducing the friction co-efficient of the rubber and contact surfaces of the wheel results in a "faster" ride. Reducing the friction in the bearings and hub along with a lower RR in the tire means that less power is needed to rotate the wheel. Thus producing a quicker rotation of the tire.

Even if a lighter wheel was used the contact oval shaped patch of tire to road would not change. Assuming no fluctuations in inflation. The oval would not change because the weight of the bike and rider remain constant which creates a "standard" oval. Lightening the rider and the bike would result in minimal gains of decreasing the contact oval.

Glad to know that I was looking in the right area of the world when I was looking at replacement wheels.