As the Newsweek article quoted above explains, GDP is not the whole picture:
"The 'perception' of higher disposable income comes from the way Americans are forced to spend money out-of-pocket on things those other countries fund through taxes and social programs. If I'm paying 50 percent in taxes elsewhere but get real benefits like public transportation through infrastructure spending, pensions for retirement and universal healthcare, then sure, it looks like taxes are higher, but the costs are bundled differently."
The fact is that, in most European countries including the UK, people generally have a better overall quality of life than Americans. Also, one really needs to visit Mississippi - or many of the poorer US states like West Virginia or Alabama, to see what real, abject poverty looks like.
As for the UK, until we come to an agreement to rejoin the single market, Brexit will continue to slow us down. It’ll probably take well over ten years to rejoin the EU, but ultimately that is the only sensible solution. Of course we’ll never regain the very favourable terms we had before we left.