Alan Joyce was not the CEO of Qantas when the 747s and A330s were ordered.
There is no such evidence to support this idea of A330s having many maintenance issues. Airbus quotes the A330 dispatch reliability at over 99% and Boeing quotes the 777 dispatch reliability at 99.3%. These are both highly reliable and mature frames, reliability is not an issue with either of them.
The new business class would have been rolled out across either option, the aircraft type is not relevant in this case.
Additionally, take a look at how the 777 compares to types in the Qantas fleet:
A330-200 (max 406) vs 777-200 (max 440)
A330-300 (max 440) vs 777-200 (max 440)
747-400 (max 660) vs 777-300 (max 550)
The 772 is larger than the A330-200, many say that the current frequencies on MEL/SYD-PER using a mix of A332s and 738s are unsustainable, particularly with the resources boom in Western Australia beginning to end.
Australian regulators have unusually strict ETOPS restrictions, making SCL and JNB nonviable with a twin. That leaves SYD-NRT, BNE-LAX, LAX-JFK and the soon to be 4x weekly MEL-LAX as the other 747 routes. This does not seem to justify a whole other aircraft type. Furthermore, the A330s Qantas have, have GE CF6s, so do the 744ERs and 767s, this commonality saves money.