I can't access the article, because it's paywalled, but is he simply comparing GDP per capita of the poorest state (which I think is Mississippi) to that of France? Is he making any attempt to account for inequality? Mississippi has one of the highest income disparities in the highest-disparity developed country in the world, whereas France (since the formation of the EU) has made enormous strides in that regard...even if the state of Mississippi generates more income overall, the majority of people in France have a substantially better standard of living than those in Mississippi. Any mention of the fact that people in France on average live nearly 7 years longer than those in Mississippi? Hell, does he note that part of the reason the US has seen sustained economic growth in the past 30 years is that they entered into a customs union with their two most important trading partners...exactly the same thing the UK left?
Perhaps he does all of those. But I've read basically this same article from Canadian conservatives with enough frequency to take a guess at what it looks like.
A related thing: as of this year, I believe that my province -- Nova Scotia -- is now the poorest region in North America by purchasing power parity. That's not because our economy is cratering...it's experiencing significant growth, because it's pretty here and (until the fires and floods started) rather mild and a nice place to live. But that has in turn touched off a massive housing crisis because supply hasn't kept pace with demand, and neither have wages. Just an illustration...here's the sale price history of a house near me:
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That's more than 500% growth in price over a span where Canada has experienced 72% inflation. It isn't even a particularly nice house!
Chasing GDP growth is pointless unless it improves the quality of life of your citizens (or if you don't give a damn about the quality of life of most of your citizens). The Anglosphere model of growth too often does not; Canada arguably does it better than the UK/US, but that's frankly a pretty low bar to clear, and much of Europe does it better than we do.
Not that GDP growth is something the UK is experiencing or expected to experience soon, mind...