"There are some that say an important feat the USA was to take a "stuffy" English language, improve it..."

If you consider lazy imprecision an improvement, I guess you might have an argument. Having lived about half my life in the UK and half in America, I find spoken UK English far more colourful, varied and interesting than American English. People seem to take more joy from language in the UK.

I would be interested to know whether there have ever been any sutdies regarding the average number of words typical of the British vocabulary vs that of its American counterpart. My guess is that that the typical spoken British vocabulary is far more extensive.