Would you call it "industrial collapse" if, following a full scale nuclear war, present day Australia was still standing a month later with little military destruction nor human casualties?

I assume you mean here if Australia escaped any direct attack? Sure. The lesson of I Am A Pencil - no one person (or country) knows how to make a pencil. Australia is heavily integrated into the world economy: to caricature, they mine iron for China, and in exchange they get everything else. Can Australia make an Intel chip fab using only on-island resources? Could it even maintain such a chip fab? Can Australia replace the pharmaceutical factories of the USA and Switzerland using only on-island resources? Where do the trained specialists and rare elements come from? Consider the Great Depression: did Australia escape it? If it cannot escape a simple economic slowdown because it is so highly intertwined, it is not going to escape the disruption and substantial destruction of almost the entire scientific-industrial-technological complex of the Western world. Australia would immediately be thrown into dire poverty and its advanced capabilities will begin decaying. Whether Australia becomes a new Tanzania of technology loss will depend on how badly mauled the rest of the world is, though, I would guess.

Even conditionally overcoming, for the purpose of hypothetical consideration, the lower prior probability of certain full scale military conflicts, direct, targeted destruction of more than about 20% of the world population as a military and strategic outcome just wasn't feasible, ever.

An instantaneous loss of 10-20% of population and destruction of major urban centers is pretty much unprecedented. The few examples I can think of similar levels of population loss, like the Mongols & Iran or the Spanish & New World, are not promising.

by pretty much everyone's inspection it's not like those who survived would be all impovershed 3rd worlders who could never recover.

But none of those countries were responsible for the Industrial or Scientific Revolutions. Humanity would survive... much as it always has. That's the problem.

Clearly there are reasons to consider prior study on the matter less than ideal, experts lacking time or funding or facing political pressure. Though, saying that experts attempted to study the issue at the time and got it wrong is different from ignoring it and from others rejecting a correct conclusion by the experts. Very few expert predictions leaned in the direction of x-risk as considered here - not just immediate near extinction but also "permanent curtailment of potential," at least when putting nuclear warfare and low if uncertain nuclear winter predictions on the same scale as other x-risks.

I've read this paragraph 3 times and I still don't know what you're talking about. You're being way too vague about what experts or what predictions you're talking about or what you're responding to or how it connects to your claims about Australia.