I think there are two differences at the moment in these boats contributing to the deficit.
1) New Zealand has better ride height control. Oracle maintains a higher elevation while upwind or on reaches. The few times we could see shots from astern with the boats underway, Oracle is almost ALWAYS crabbing with the bows pointed 5 to 10 degrees higher than their direction of travel...which means that AOA of the foils is higher carrying more drag, the apparent wind angle across the deck is more steeply angled, they are closer to a sideways stall putting them at higher risk of a big slide slip like we saw during the first leg of the second race yesterday. The good news is that that ~should~ be correctable given enough time - but I'm a little shocked they haven't already discovered, dissected, and solved this problem. I've noticed them crabbing quite a bit from the very beginning. It's probably a combination of control system and technique...but it DOES appear that Spithills steering wheel was changed at some point to Team Japan's style of twist grips that are presumably for ride height control....I'm not sure when he started using that but I'm pretty sure they didn't start out with that setup.
2) Possibly, wing control. I have always felt that Glenn Ashby was going to be a very quiet secret weapon if he was given the control he needed being one of the few honest champions of apparent wind sailing on these teams. I'm dying to know what all he is controlling from his tucked away cockpit. New Zealand is the only team without a winch and even their mainsheet control is push button hydraulics. They don't observably move their wing nearly as much as the others and other teams seemed to have slowly followed suit with fewer and fewer mainsheet wing movements as the event progressed. I suspect (this is pure speculation on my part) that Ashby is making smaller more localized and precise wing trim adjustments inside the wing where other teams were using the mainsheet to make less efficient course/gross adjustments to compensate for trim and power. If this is the case, this will be harder for Oracle to develop and match as it's dramatically complex and would require a great deal of acquired skill (time) and talent.
Oracle is not in a good spot right now - unless the crabbing issue is fabricated and they're trying to make things dramatic, which I highly doubt. They're going to need to come out winning immediately next week if they stand any chance at retaining the cup.