The consideration of standards of living is not an end all for considering geopolitical policies. In the UK, one may look back to the Clement Atlee government as an example of poor public policy, as today one may look to the influx of economic migrants, neither of which correlate to reserve currency issues.
As to per capita income internationally, may I suggest looking at: https://worldpopulationreview.com/country-rankings/median-income-by-country
If the US's relative place in the world is a matter of reserve currency, then Luxembourg, United Arab Emirates, Norway and Switzerland have something other than reserve currency status to explain their position above the United States.
But since the US has its poor, so distant from the US's most affluent, the notion that "too many differences" between nations is about currency or modern monetary theory. Additionally the massive US debt is become a glaring issue, as our service economy makes little steel compared to China, as one example, among many. Perhaps we all have been counting economic progress with incorrect measures?
Certainly, a "loss of geopolitical importance" for the US in ongoing under the Biden administration of which moves away from US currency transactions are a symptom, not a cause.
What I find fascinating is that in the US the highest media income and related metrics cluster around DC, besting even the "best" of the individual states. Ah, government. It feeds itself first and well indeed. At all levels and all acorss the globe.
As a bonus to the discussion: "A €600 million renovation plan will see the seat of the German chancellor balloon to be larger than the White House or the Elysee Palace. But why might Germans be opposed to their leader's seat of power being too grand?"
https://www.dw.com/en/germanys-lavish-plan-to-expand-berlin-chancellery-faces-controversy/a-57275022
Seats of power. Where the fat cats sit. The "ordinary" people have little to benefit from "lavish plans" and such seats of power.
Regards.
Yes, I referred to "standard of living" as a quick and easy proxy.
As for Luxembourg, United Arab Emirates, Norway and Switzerland: There will always be strange outliers; their rel. wealth is easily explained:
Lux. is essentially a large urban area, with little hinterland. Urban areas always outpace equiv.-sized rural areas. They are safely ensconced in bigger countries that bear a large share of the, e.g., defense burden.
U.A.E.: Oil.
Norway: Hydrocarbons.
Switzerland: Similar to Lux.
Common to them all: The lack of a certain demographic.
Regards,