Angryrat, I take your point, but dumping is not exclusively an act caused by another sovereign state...private.companies are the typical culprits.
The anti-dumping laws, very broadly summarised:
"Both the Australian system and WTO agreements focus exclusively on whether dumping and/or subsidisation has occurred, and whether this has caused or threatens material injury to the local industry producing like goods."
Material injury could mean reduced profits, which it could be argued Jetstar NZ causes AirNz.
Certainly Qantas may be harmed by a robust Virgin, but it does enough self-harm that it would be a an interesting argument. Under its current management Qantas could go bankrupt even if there was no external competition.
Qantas does not compete on a level playing field. No question. But that seems to be a particularly Australian affectation. No one else in the world cares about perceived fairness as much as we do. On the other hand they all seem to have governments who don't throw up their skirts to all comers.