I doesn't seem that navigation was the issue, in this instance. (other than (possibly) not finding the bivvy. we don't know that for sure
How often is it SAR incidents have arisen due to navigation on the tops? that question needs to be understood.
The Tararuas are a bit different, in that because of plenty of alpine travel at relatively low altitude, a number of "classic" trips have evolved. These entail tops travel carrying packs on nearly all of the main ridges . the hut system supports this. so frequently the tops are high risk. and often, theres no quick exit with using these routes.
In the past, there has been a strong resistance from the many tramping clubs in the region, NOT to sign post and pole the tops.
As @philipW says, there is a risk off more inexperienced people taking on trips that are beyond them
I am inclined to agree.
Difficult to locate huts like arete should probably have the immediate routes poled. But theres very few huts like that location.
Probably poles or signs on key track junctions are warranted. eg, Junction Knob, Pinnacles Spur. But even then, a simple pole or two may be adequate.
There been a creeping poling of the tops, by DOC. ie Main Range, Powell Jumbo, Southern Crossing. Even warning signs at natural 'hazards' like BA Pinnacles.
If tops poling is going to create the idea that the route is ok for the inexperienced, then my view is no, don't pole the tops.
I think theres been a gradual increase in tramping of the interior routes, arising from the easier routes around the fringe. ie Field track, Powell, Atiwhakatu. Herepai, tauherenikau, etc
Encourage more, to go further, and where does it end? In places where poling tops is irrelevant. Hypothermia can strike, regardless.
PS; there were signs and poles leading to Kime, where Bennington came unstuck as I recall?