It wouldn't have mattered what level the radar at McMurdo gave them clearance to descend to. All the radar was concerned about was traffic in the area and in prior briefings AirNZ had been told they would receive no support from Radar whatsoever.
The whole idea that any clearance to descend by the briefing officer or radar or the baggage handler at Auckland airport absolves the crew of their own duty of care to their pax is ridiculous.
There is a saying in aviation and any safety led industry "If there is any doubt there is no doubt" The fact that we are debating if the weather was good enough says it all.
And if it makes you feel better then sorry, 2000 ft in marginal VMC, in a widebody jet, at 5 miles a minute, over featureless terrain, including a 12448ft mountain and next to that a 5948ft peak that they also could have hit, while without radar, or any way of updating their maybe 3 miles an hour drifting INS, is still not safe.
Collins let corporate pressure influence him and a false sense that his prior experience enabled him to justify the decisions he made on the day. Any commander has the right to operate outside of the SOPs as he sees fit, if and when required for the safety of his passengers and aircraft. In this instance Collins operated well outside the SOP for no justifiable reason and the accident occurred.
"But thick here eh Bert"