US's lifespan is not caused by lack of access to healthcare though, that is fentanyl.
True, however Australia has a tiered health care system with a very low gap to ensure that practically the entire population has access to healthcare that they can afford in addition to national bulk pharmacy deals to cap generics for the bulk of ailments that require prescription.
For all it's warts the Australian system delivers a kind of healthcare that the US system does not .. widely available affordable treatment for the bulk of medical issues.
US (general mean both sexes) life expectancy sharply dropped as COVID spread, the most that fentanyl can be accused of is the flattening of the general slow increase between 2012 and 2018 .. even that ended and was on the increase until the USofA foot gunned its handling of COVID.
[ Historic USofA ] https://population.un.org/wpp/Graphs/Probabilistic/EX/BothSe...
[ Historic Australia ] https://population.un.org/wpp/Graphs/Probabilistic/EX/BothSe...
How do people with substance use disorders stop using substances? They use healthcare, unless they're in the US where they'll using some quasi-religious abstinence-only residential programme.
[ raw data source ] https://population.un.org/wpp/
So it appears that both Australia and the UK with National Health services (named differently in AU) have greater life expectancies than the US.
Perhaps it's the authors you read?
Bertrand Russell was 97 when he died.