While I think the scale of American decline is overstated, I think there is a degree of Hemingway's law of motion.

A desired task that requires the most skilled makes those skilled people in demand. If a power has significantly more resources then they have more to offer those most skilled people.

It isn't at all disputed that there are a huge number of scientific discoveries that have occurred in The USA by people born outside the USA. That shows the draw of that power, but it is a relative draw. As the ratio becomes smaller the draw is less.

Advances like this are a feedback mechanism, being ahead gives you more resources to stay ahead.

If you consider the average contribution of advances to be a relatively steady force advancing a nation, yet a nation is in decline, it stands to reason that the decline is in another area and is being mitigated by the advances.

If the force propping things up goes somewhere else the change can be quite swift because the force of the decline becomes suddenly much more apparent.

I don't see the world going full Mad Max, but I can certainly see a sudden shift to the USA being considered no different to the UK,Japan, or Germany.