The initial conjecture is that the US' "Adversaries see [wasteful profligacy] as weakness." We have established that the US seems to spend wildly with muted negative outcomes. To an adversary, should that be seen as a weakness or a strength?
Could things be better in the US if it did not spend the way it does? That is a difficult counterfactual. The well adapted US political system never voluntarily decreases taxes, so a safe assumption is that spending/deficit/debt would be the same.
A significant amount of war funding was spent on the MIC, which employs upper middle income US persons in engineering, logistics, HR. The rest is spent on consumables (also from the US) and bribery, which eventually finds safe harbor by holding large bricks of US $100 bills on the low end or US luxury dwellings on the high end.
In the counterfactual, what would have happened to all those white collar suburbs and Miami penthouses?