[Barrin92]

For one on a data level that's not an accurate statement even limited to the countries in question, here's productivity: https://ourworldindata.org/grapher/labor-productivity-per-ho...

Europe has largely converged on American growth, the East in particular continues to grow fast. But more important is that this is obviously an intentionally selective group of countries. Add Taiwan or South Korea to this story and it becomes a lot more complicated, because the latter is about to/has overtaken Japan on a per capita basis while having some of the worst demographics on the planet.

There's research by Keyu Jin that actually shows the opposite, globally growth after the year 2000 has been faster in aging countries for the simple reason that it increases returns on labor saving technology, i.e. automation (telling image:https://cdn.statcdn.com/Infographic/images/normal/13645.jpeg) and that is, even if you are conservative on technological developments in the next few decades, likely to accelerate quickly.