63% probability of a 60%-80% decline in stock prices within two years? Really? (And, given that, why so little probability attached to a smaller decline? What's the underlying model here?)

Systemic overvaluation of stocks relative to risk as a result of tax benefits combined with overdue bills from the last three economic shocks. The full extent of the drop will require including inflation in consideration.

And what exactly is OrphanWilde's mental model of the WHO's attitude to US healthcare, that predicts such a huge influence of the existence of a US national health database on how the WHO assesses countries' health?

It's not the WHO's attitude towards US healthcare, it's a difference in attitudes towards national pride between the US and... everybody else. In the US, outward patriotism is combined with criticism of our institutions; representatives of the US are all-too-happy to say what we should do better, but still insist we're great anyways. Elsewhere, it's dangerous and right-wing (in the European rather than US sense) to be outwardly patriotic (unless the government is dangerously right-wing already, which is to say, requires patriotism of this form), but that gets combined with a resentment of any implication that there's anything wrong with their country or culture.

So ranking systems tend to accentuate the things Europe (which is powerful enough to get its say) does well (such as national health databases, repeatedly, for every category of health) while making sure the US ranks below them so they can say they're doing better than the central modern superpower (because Asia doesn't count and nobody wants to annoy China).