Premium class redemptions to Oz are terrible value.

Malaysia would have sold you a cash ticket in J, ex London, for £1500 in their January sale for travel on any date until mid December 2017. Why blow 300,000 Avios (more if not on BA) and £700+ of taxes?

You can always get Oz for under £2k if you don't mind an ex-EU, eg China Southern ex Amsterdam. I looked this up last December out of interest for a departure 4-5 days later and there were quite a few options.

Last time I checked you could still get MH via Expedia for under £2000 as long as you booked a £7 hostel for a few days as well as part of a flight and hotel package. I have not rechecked this price for the last 3-4 weeks though.