Key vs Ardern
This chart shows the Preferred PM ratings for John Key and Jacinda Ardern at the same stage of the terms as Prime Minister (Month 1 is Jan of the year after they were elected). In their fourth year of office they were polling quite similar but in this fifth year Ardern has dropped month after month and is now 10% below where Key was. And in fact Key remaining in the 40s or very high 30s right up until the end of his eighth year in office when he retired. He never ever polled as low as Ardern now is.
So maybe it is time for some media to stop referring to Ardern as being supremely popular!