QF used to do this route CNS-DRW-SIN with a SP which was always pretty full. Then it went to a B767 because the SP's were retired and it was still pretty full. Then AO took the route over (I don't recall AO going SIN direct, I may be wrong) and it was still pretty full and I would assume the yeilds would have been about the same or a little better than when it was a QF 767. What this did was allow QF to increase their ADL-DRW-SIN flights. Some days now there are 2 flights ex DRW to SIN within about 1/2 of each other. One ex BNE and I think either QF81 ex ADL or the flight ex CNS.
These are just the changes that I have seen on this route over the last 6 years, no doubt there will be more. But looking at the whole picture, I still don't see how Jetstar could make more money on this route without using the A330.
Also over these years the flight is one that consistently has a high load factor 75-80% and is always full of cargo. If this flight is not making money then that is a management issue, as it always full of cargo and has a high load factor it should be making a good profit. If we are not charging enough for seats, the Pilots,FA's and Ground staff can't be blamed for that. That is a mangement problem.