That was a really good read, thanks for sharing OP!
The topic of UK being as poor as Mississippi isn't really the main gist of the article. It is the title and discussed in the first paragraph, but the article isn't really hung up on it.
I think the main topic is about country divided. London vs "not London", haves and have nots, those who were winners of various past policies and those who were left behind, and how that has shaped the country and its politics.
The decline in living standards is sobering read - the extent of child poverty is abysmal, and how is the average pay for junior doctors and civil servants just a little bit north of £35k, when minimum wage is £25k? At the same time 100s of Millions have been poured into cancelled infrastructure works and bat shelters and what not, and taxes are higher than ever. We've all been screwed right left and centre paying the money through taxation for all these failed projects whilst essential health care staff are paid a pittance.
It also highlights how lack of strong leadership (including moral) has left the country and its institutions vying only for their own (and their cronies) benefit, and in complete disarray. Nobody knows what the common goal is, there is no cohesion or teamwork, everyone is pulling to different directions. Reform may think (or do they?) that they're working for the benefit of Britain, but all they do is sow seeds of discontent and fuel hatred and violence. They also are just more of the same - playing party politics and keeping eyes on the price (power). They do not work for you, they work for themselves.
The article is a good read for anyone who isn't restricted by paywall (you can read it if you haven't read any other Atlantic articles this month). It does paint a bleak picture, but it just verbalises how I've felt about the UK economy for such a long time so, so well. Hits the nail in the head.
Thank goodness I have an Irish passport as well (sorry), may need it soon!