The UK empire is considered by many to have ended in 1947 with the independence of India. Others say it was finally finished in 1997 with Hong Kong. Either way the UK is still around and while things aren't rosy, they still trudge along and will continue to do so.

Meanwhile the US's "supposed upcoming ending" puts them in a better position than the UK was in many different categories. It still has massive resources, amazing talent and a citizenry with an "ambitious" can do attitude vs the "tall poppy syndrome" of the UK. Its difficult to argue that there is an exact end date thats occurring now. To say its all over and that there isn't a second story coming seems premature.

Re China: This is a country that has overexpanded in infrastructure which will come home to roost sooner or later, has a terrible demographic structural collapse looming with no realistic way to correct(unlike the US which has options to correct), has overinvested in so many industries that they are experiencing massive (25%) youth unemployment with deflation occurring. They have serious problems coming in the next few decades.