The America's Cup Class rules aren't all they first appear. A measurement system to stop oversized sail with the use of leech hollows has be turned on it's head to produce tiny batwing mainsails.
Meanwhile, for the light winds there is a hole in the maximum sail areas. The rule assumes 26.5m sail height, but we already know ETNZ has a longer mast. More free sail area for the enterprising kiwi's.