I understand the valid point the OP was making, but this is a hardy perennial argument which surfaces regularly. As only one other poster appears to have mentioned, we are talking about two different things.
Health care, per se, (as in the quality of procedures and research,) is probably second to none in the USA (as one would reasonably expect in the wealthiest society on earth).
To what the WHO, and a number of other organisations, are referring is the health care system extant in the USA - primarily concerning distribution and availability (related to the ability to pay). For different reasons, (but still related to distribution) Australia fared badly (only a few places above the USA) in the WHO rankings. This may sem unfair to Australians (Australia offers first class medical treatment, combined with an effective UHC system,) but its overall effectiveness is reduced by the tyranny of distance. This means that a relatively few people living on a land mass slightly larger than the continental United States, experience difficulties in gaining access to prompt services due to having to travel literally thousands of kilometres (in some instances) from extremely remote communities. Thus, the distribution of health care services is unequal depending upon where you live. (People elsewhere have little concept of how large Australia is - Texas would fit about six times into one Australian state - Western Australia.) All these things are valid arbiters of a health care system, but not necessarily of the quality of health care offered.
I am not nit-picking, but trying to assist in the understanding of what was meant by the OP, and the reaction of most Americans to the apparent allegation that US health care is sub-standard. It most decidedly is not, but perhaps the system could be improved.