So what in this description sounds so implausible? Is it that you think productivity growth will come in at 3 percent? That it will all be worth it because advances in medicine will allow us to stick around in decent form until age 135? That technological breakthroughs will extend the reach of the U.S. military further yet? That the Mars colony will be awesome?
Just how lucky are you feeling?
Given that we keep being told we will be supplanted by another rising power and haven't yet, I think the past is a pretty good track record for a bit more optimism.
The major flaw with predictions like that is that they seem to assume that no other country that competes with us will falter or slow down with their own problems. As Kipling wrote:
Man cannot tell but Allah knows
How much the other side is hurt.
Even if every glaring problem the author assumes for America comes true, don't assume our competition has no problems to overcome just because we don't see them.
Competition involves comparing America to other countries. That's the implausibility of the prediction of America's decline and fall. Luck has nothing to do with it.
