You haven't convinced me.

Weight in the bow when going downwind in light
air would reduce wetted surface. This could be
accompished by shifting other internal mass,
including crew weight forward, or even better, by
use of a swinging/canting keel.

Wetted surface can also be reduced by inducing heel.

I can see how punching through a contrary swell
would be improved with ballast, but this could
easily be accomplished with athwartships ballast
tanks.

The best place for ballast tanks is in the aft flared
section of the hull where it will exert the most
leverage, and heel can be controlled by choosing
which tank or tanks are filled.

I don't know of any boats with built-in bow ballast
tanks. Do you?

OzOne wrote

And it would be downwind if the yacht was fitted with bow tanks.