It's delivering more horsepower than the normal diff because it isn't binding or slipping. Besides avoiding the inefficiencies of traditional designs it is also giving race teamS the huge advantage of not having one of the drive wheels spin out of control.
Considering the blown engines, shorts inside fuel tanks and cobbled together brake systems, I'm not surprised the same team that crippled their diff cooling system for a qualifying run, missed getting the diff cooling setup right. As I said, judging from their enthusiasm for the extra mph out of turns, they will use whatever fluid/radiator combination they have to in order to keep the Iso-Torque happy. The bottom line is this racing team has gone on record as saying that a heavy, down on power compared to other racers, formally not that competitive, racing 350Z has a shot at being a winning racer largely due to a new diff design that lets them have a large advantage over other racers. That's my reading of the tea leaves. Others have a more dismal take.