To me, it's adolescent logic to argue that our strengths are our greatest weakness.
The perception that the US has fallen is exaggerated by half, but clearly execution failures, spectacular to mundane, are all too pervasive. Have we just gone pear-shaped? Tits over tea kettle? Lost our mmmmmojo?
One theory is that the rate of failure is unchanged, but in this age of information, they are spectacularized whereas century ago they would have been squelched.
Another theory is that the US has run out of easy wins. Once, oil literally oozed out of the ground in downtown LA. Now, we install rigs in the harshest of locations and must poke miles down into the earth ... or just deal with the Devil. When electricity was first harnessed, options for exploitation were limitless. Gains were huge. Now we must conserve. Innovation used to happen in leaps and bounds as we thought up brand new things. Now it's a slow climb up a steep mountain, figuring out how to do the same old things incrementally cheaper, faster, better.
Or perhaps a social evolution theory applies: Humanity was once, by necessity, survivalistic, decisive, ends-justify-means, hunter-killer, red meat, Western, wanderlust, and masculine. With innovation and social organization, that necessity has abated, being replaced by new imperatives: collaborative, change-averse, risk-averse, non-confrontational, agrarian, vegan, Asian and emasculated. We've evolved (socially) to a point where we believe that our best chance for survival lies not with our individual abilities, but is tied to our capability to integrate within, and enjoy the shared bounty of a larger society. In order to push the whole society to produce and achieve, each member must first endure the necessary overhead of "connecting" with the other members. To "connect" one must spend time communicating, documenting, justifying, persuading, organizing, planning, coordinating, motivating. I'll lump these societal requisites together under the term "connecting."
As the theory goes, people now focus so much on "connecting" that they run out of time to actually produce. This sea change in the way of getting things done (or not) causes a black hole which swallows great people, ideas, laws, and businesses before they can create anything of value.
If you don't like that theory, you could just say that we've just become rich, fat, and lazy. In his case, you must conclude that, just as the Romans, the Akkadians, the Hun, the Mali, the Egyptians, the Ottomans, the Spanish, and the English, so will the American empire fall.
It doesn't much matter which justification you prefer. What I would like to figure out is where we go from here!