One difference is that the U.S. system gives a lot to the people who pay a lot. Rich people have access to the most advanced cancer treatments in world, for instance. But child mortality is relatively high among poor people (which is a shame on US.).
Of course, this is indeed bad for efficiency, if you consider health outcomes vs. spending. And inequality: wealthy people live longer. But then there are questions of fairness.
Elsewhere, in a so-called welfare state where I live, all children get very good care and child mortality is low, but for instance, when I consider myself - a fairly well-to-do person although not wealthy by US standards - I pay a lot to the system but it gives me very little attention. No regular health checks that are normal in the US for people who have a health insurance through employment, no screenings for cancer (women get several types of specific screenings but men do not).
(We use 9 % of GDP to public health, vs. 17 % in the US.)
I know that the care is quite good if I run into a life-threatening situation, but with smaller trouble such as broken bones or a pneumonia, I'll be prioritized down after drug addicts who have a more serious condition that they have inflicted themselves. And they never contributed to the system which tells me to go to a private clinic.
Fortunately the social problems resulting in non-contribution are still quite small, but an increasing number of people are not giving anything and are consuming more and more of the resources.
