I'm curious to understand why you'd think a law passed by elected lawmakers is more durable than a verdict by judges who have their position for life? Obacare was surely very controversial, but despite the best efforts by the conservative and an ideologically hostile Supreme Court, it remains in place after ten years.
Those efforts were actually pretty half-hearted. They talked a big game, but they don't actually want to abolish it. (Reminds me of how the UK doesn't really want to face up to a no-deal Brexit, despite lots of brave talk. Or how no government in the UK has so far re-nationalised the railroads, despite re-nationalisation perennially polling high with the general public.)
Legally, Parliament could repeal it tomorrow and ban same-sex marriage again. Politically, that would be impossible without another plebiscite, and there is no reason to believe a new plebiscite would deliver a different outcome; it would almost certainly return the same result, and likely by a bigger margin.
No conservative politician in Australia wants to talk about this. I'm sure some of them are still personally opposed to same-sex marriage, but they all realise trying to repeal it is hopeless, and so they'd rather talk about things that they have some hope of achieving.
The realignment of the Court, plus this Court's willingness to overturn settled law, together signal that a new law prohibiting same-sex marriage might be allowed to stand if brought before today's Court, returning the US to a country where same-sex marriage is not universally legal.
So I would regard our current regime around same-sex marriage, civil rights, etc. to be subject to not being directly challenged at the Supreme Court.