Historically, it is very rare that a government only has 1 term - they usually get around 3 terms before the public tosses them out. For Luxon to be so unpopular that they are staring in the face of electoral defeat this early on in the process means that he has undeniably fucked up really bad.
I don't think RNZ is being biased on this, there is absolutely fire somewhere behind this smoke. If National weren't such a hopeless pack of incompetents they'd have rolled him by now. But at the moment their strongest contender is an ex tobacco lobbyist (Chris Bishop) which really says something. Ever since Key left they haven't really recovered.
Hopefully they'll keep Luxon and get completely steamrolled.