The first part of that reply form the CSR is total and utter rubbish. You are allowed 4 segments and 2 stopovers in SWP either at the end or the beginning of your itinerary as you wish. The restriction on "transcons" is there to stop you doing SYD-PER-SYD-PER-SYD as a mileage run.

The CSR seems to be trying to reinterpret the rule as:

WITHIN AUSTRALIA - ONLY O N E NONSTOP/SINGLE
PLANE SERVICE IS PERMITTED. THIS MAY BE BETWEEN THE FOLLOWING
POINTS:
BNE/CNS/SYD-PER;
MEL/SYD-DRW.

But there is nothing that limits this rule to tickets originating in SWP, so if her interpretation were correct then it would apply to tickets issued anywhere else in the world and people visiting Australia as part of, say, a xONE4 issued in Europe would have the same restriction, which is clearly ridiculous. (And what's more you wouldn't be allowed to visit any city except those listed!)

The OW rules are fairly precisely drafted. Unfortunately, English comprehension and logic are not compulsory requirements to be a CSR (or Industry Support rep). Curiously, I actually find that non-native speakers of English are better at this, so given a choice I would always pick the fluent non-native agent rather than the native speaker if I need to explain some specific point in the rules.