I thought it went more like this.
C17. Flies into international capable airport. Somewhere with refueling capabilities, logistic capabilities to handle C17's. So this would fly into the country (say Dili airport East timor). Sydney to Dili, Brisbane to Dili etc. Backbone of logistics (with sealift), able to move trucks, APC, tanks, bulk ammunition, etc. Its secure, it can handle this type of aircraft and 100's of tons of cargo. C17 is just doing the biggest economical flights not going over risky airspace dropping a single pallet to a platoon in the jungle.
C-130 does smaller flights direct to regional airports, darwin to Baucau etc. Things like medical, specific munitions, light vechicals (cars, bobcats), food, etc. The requirements for 10's of tons of cargo.
C-27J is your intra theatre lift, Going from Dili or the regional airports to bumfruk WWII strips. Part of the logistics train in the country your operating in. Moving some of the resources from Dili to those regional airports or to bumfruck. Medical from some arse end strip into some major hospital in the country. They might drop off a couple of tons of cargo and might do multiple stops/drops on a run. Cheaper to run than a Chook, faster than a chook, cheaper than a C-130, gets into tighter areas than a C-130.
You chook then does intra theatre vertical lifts, medical out of the jungle, dropping 155mm + supplies on mountain tops, operating to and from the LHD (which I would imagine would be a major medical centre in places like ET where there is basically nothing) etc.
Obviously when working with the Americans, everything changes. They probably use C-17 as intra theatre lift on some WWII airfield they have completely paved in a few days. But hey when you have 100's of the buggers you can. But when operating with out them, or with minimal US support we can offer a full range of airlift.