Generally I am in agreement with your thoughts and we are splitting hairs. Travelling an extra 4 hours would not be a big deal for me, 7 might be.

I just prefer a service that runs daily. When travelling to Africa it becomes even more important as there are few alternate choices out of some locations if there is a problem with one carrier's equipment. If you are connecting to a transoceanic flight it's nice to know you won't be cooling your heels for several days waiting for the next flight.

Begging to differ on the number of flights--but I just checked on Qantas and it is still only 3X a week on QF63 from SYD/PER/JNB and 1X per week on QF23 via HAR SYD/PER/JNB. Melbourne is not listed other than as connecting to QF23 or 63 via PER. It seems to be discontinued (it was in earlier schedules but does not show now). Maybe it is a seasonal route?

The total travel time (including brief layovers) from SYD is 17 hr 15 min to 19 hr. 55 min depending if you stop in HAR. I agree if you are in Perth that there is an advantage to Oneworld to get to Africa (and there are other advantages of Perth too!).