I suspect the old adage of supply and demand comes into play. Since EK started EDI last year, EK pax throughput at GLA has dipped around 10% -15% on a month by month basis prior to the addition of the A380 at GLA. Therefore more competitive pricing would make some sense compared to MAN. Whether the addition of the A380 has helped to reduce the deficit in pax numbers, remains to be seen.
The 777 used to operate the direct AKL when the route first started, so the old girl can fly the route non-stop, as do QR from DOH. The DPS stop was created purely for commercial reasons and to provide a link between AKL-DPS, as no one was operating the route prior previously.