So what do you think is a fairer way to measure governments? Ratio of important successes to important failures? A matrix of weighted policies and implementation scores?
You'd probably end up with something similar to to the UN's human development index (http://hdr.undp.org/en/composite/HDI), in which the US ranks #17, behind Norway, Ireland, Switzerland, Hong Kong, Iceland, Germany, Sweden, Australia, Netherlands, Denmark, Finland, Singapore, the UK, Belgium, New Zealand, and Canada. All of those are perfectly livable countries. My only criterion was "developed democracies", and Hong Kong isn't even much of a democracy anymore. I don't think that's an unreasonably high bar.
Our government is just on the low end of mediocre compared to other developed democracies, at least by the metrics I can think of.
If you can think of a better metric, I'm all ears.
Also when you excluded say Nigeria and in fact most counties then every remaining country is going to seem worse simply because you just arbitrarily raised the standards. It’s not US exceptionalism to simply say few countries or groups of countries have landed anything on Mars which is freaking difficult. Sure, providing great healthcare is more important, but it’s also something very few counties have done well.
In the detracting from success by looking at unrelated failures misses my argument, at best it speeks to the likelihood of success not the possibility.