Seriously??? A premium airline shouldn't have mechanical issues?
ALL airlines have mechanical issues from time to time. If you want to fly on something that never has any mechanical issues get a magic carpet, or some other mythical mode of transport.
A premium airline should be able to recover the situation and get the passengers to their destination in a reasonable timeframe or appropriately accommodate them until that point. In the instance you point to Qantas did just that.
As you have pointed out many times, you choose not to fly Qantas, yet you are oddly consumed by their perceived failings. Instead you fly on SIA and AirNZ, well believe it or not, they also have mechanical issues and turn backs from time to time.
Even though they are premium airlines!!
Hard to believe I know, so here are a few examples;
SIA A380 air turnback 2014:
Singapore Airlines A380 forced to turn back mid-flight - CNN.com
SIA air turnback 2014 due air-con fault (sounds familiar):
Singapore Airlines jet returns to Changi due to faulty aircon | The Indian Express
SIA A380 air turnback 2012:
Singapore Airlines A380 turns back after engine problem | Reuters
AirNZ AKL- HNL air turnback 2014:
Air NZ flight forced to turn back | Stuff.co.nz
AirNZ AKL- SFO air turnback 2014:
Engine trouble forces Air NZ flight to turn back - News - Travel - smh.com.au
AirNZ MEL - AKL air turnback 2014:
'Rocky flight' before Air NZ emergency landing | SBS News