I have to say that's a very odd way of calculating it.
On my end, buying 52.5k Aeroplan points is CAD$1,125 (30kpts + 22.5k pts bonus)
+
The taxes for a business class seat is CAD$191
= CA$1,316 =~ AUD$1,325
Just because you're buying points on special and then converting it to c/pt, it doesn't mean that the money spent goes down (ie $1.3k spent doesn't magically turn into ~$1,050).
Likewise for QF points whilst on special too - what you pay is what you pay.
For a MEL-SIN business class reward seat, it's 82.1k pts. With the current special you'd need to buy 70k pts for a 17.5k pts bonus = 87.5k pts for AUD$1,919. Add on taxes and it's over AUD$2k for a reward seat. Still cheaper than a regular cash fare of >$3k+ though and of course subject to actual availability.
If you can show me where I can spend $1,050 actual cash (disregard c/pt, or any other irrelevant calculations) for a MEL-SIN/CGK one way business class fare, when it costs ~$1.3k/~$2k to purchase AP/QF points whilst on special / taxes, I'm all ears!