Planning a RTW trip including a flying from SYD to the South Pacific, preferably PPT.

Can somebody please be so kind to confirm that this is doable with the Global Explorer fare and that BA's information that "oneworld don't fly to PPT, not even code share" is to be dismissed as a mishap on the side of the agent I was speaking to?

Many thanks.

Oneworld does fly to PPT.
There are Qantas codeshares on Air Tahiti Nui linking PPT westwards to SYD and AKL, and eastwards to LAX.
And there is LAN on LAN metal linking PPT eastwards to IPC and SCL.

OneWorld Explorer fare allows only the LAN flight, and because it crosses continent barrier, you cannot take it twice. Therefore no PPT on xONEx

Global Explorer allows for those three codeshares, therefore you can go to PPT from west (SYD or AKL) and leave it again to west (SYD or AKL), or leave eastwards (IPC,SCL or LAX). Again you cannot go twice eastwards, as it crosses continent zones (TCx).

Therefore PPT is available only on GLOBEx, and valid routings are
SYD/AKL-PPT-SYD/AKL/IPC/SCL/LAX
I would definitely recommend going PPT-IPC-SCL

I thought TN flies to SYD and AKL (and not MEL). QF does codeshare both these flights.

Mea culpa, at one place I put MEL.
Correct flights are PPT to SYD,AKL,LAX