Thanks for your detailed thoughts on this, Omoxiedot - and interesting what you say about the problems of the past fifty years, as well.
I'm only in my twenties, so looking back to perceptions of America in the twentieth century is doubly speculative - I knew neither the time nor the place. But my feeling is that Britons had a degree of admiration (or at least awe), rightly or wrongly, for the US of the 80s, for example, in a way they don't now - with the clear and terrible exception of the racial problems that have plagued the US and many other countries for decades.
No country is perfect and so any presentation as such can only be a facade, but my own personal feeling is that the glossy outer image of "perfection" that the US once presented to the world is growing more transparent, and it is easier to see some of the problems that lie within.
And I certainly agree with you that we shouldn't be aiming to be the best in respect of any kind of global ranking. Governments should aim to do the best by their own citizens and be cognisant of the variety and differences within that group.