You must know the only we we can have Covid zero is to stop all incoming.
If we were relying on NT as the only route home, then we would be bringing back only a fraction of the number of Aussies that we have.
Of course. But people were saying covid zero is impossible. As you say it is possible if you stopped arrivals.
If all the Aussie overseas had come home when they were advised to do so - early on, cap free, home quarantine - we would have reached zero after the first wave or so, and lived our lives relatively free waiting for the vaccine to be rolled out.
But there was a large cohort of those overseas who didn't want to come home... they had just started a new job, or were on a working holiday, or didn't think this was serious, had to give notice at their current job, or still had two or three months on their apartment lease. Then they got stranded. Now they trickle in and some of them are bringing covid.
If the borders were truly closed, save for compassionate cases, and other measures such as a Singapore hub were established for air freight, we could be relatively close to covid zero. (Even freighter ships could berth without crew coming anywhere near land or other people.)