UH-1 in Afghan
"may have been chosen for its role due to better hot and high performance than the much heavier twin-engined Super Huey or Blackhawk."
The US State department uses the Huey as part of its arsenal against the poppy trade which is mostly limited to the plains south west of Kandahar in Helmand provence (about 3000' AMSL). They also operate clean skin most of the time with less than eight troops on board (about four in summer).
The Super transporters were able to operate at 6000' AMSL with eight passengers (not combat troops) with no armaments or protection systems on board. Hence they only operate to secure bases with a low threat level. They did perform better than the Puma's in country in the hot and high environment (not Super Pumas, EC 725s or the NH-90 and definitely not the S-70).
You can also hear them at ten miles (20 if the wind is blowing from the right direction). Might not have been a problem in the jungles of Vietnam but is a major problem in the sparse terrain of Afghanistan.
As for the importance of humanitarian or DACC work by the ADF. It is only done because the assets are there and is not a selection criteria for the platform. There are plenty of civil companies who can fill that role if needed and who would be more than happy for the work. The ADF gets called in because the tax payer has already paid for most of it so it gets better value for money than getting civil companies to fly half way across the country.