Again, the premise that Australians are paragons of health is incorrect. It's a fairly fat country. Australian men literally only rank behind American and Chilean (random) men in likelyhood of being overweight.
What’s your source for that? The list of countries by BMI has us tied at 43rd with Canada, behind the US (16) and the UK (39).
https://en.m.wikipedia.org/wiki/List_of_countries_by_body_mass_index
In my observation it is a lot easier to come across healthy food here and there is a more active culture (it’s not uncommon for people to play community sport into their late 30s). Which is not to say the healthcare system does not deal with a reasonably significant number of chronic illnesses, but I’d be surprised if it was on par with the US.
Diabetes does not seem as common and I legitimately cannot remember the last time I saw an overweight person using a mobility scooter, whereas in Florida that felt like the preferred means of non-vehicular transport.
I would have been inclined to agree that the general health of the population is better (not just in terms of chronic illness but also the ability to get access to a doctor earlier to avert the worsening of certain conditions), which may have been a factor in the fact we’ve only recorded 74 deaths to date where I understand the youngest to be a man in his 60s.
In saying that, there is obviously a lot of data to still be uncovered in relation to viral load, strain and optimal conditions for transmission. So who knows if any of that has played a part too.