From AKL it is a significant extra time to fly via SYD/MEL/BNE to go oneworld, however another option is Air Fiji via NAN to LAX, connecting to AA.
From WLG it is still longer flying via SYD (QF operates WLG-SYD) than via AKL on Air NZ, but the time difference is not as big as it is ex-AKL.
The only other fairly direct options are Air NZ or Hawaiian for AKL to HNL connecting to AA, or a much longer routing on LAN for AKL to SCL then onward to USA.