The US has (without much debate) the absolute best healthcare on Earth if money isn't an issue. There are so many more experts in so many more fields with access to so much more cutting edge technology that...well rich people travel to the US to get care.
Yeah, what does it matter that the best healthcare, only available to the globally rich, American or not, is in the US?
A much better measurement of a given country's healthcare system in more meaningful terms is average outcomes of the whole population, like life expecrsncy, child mortality rates, etc.