It is a myth to suggest that “the United States benefited economically” from WWII. It’s true that the economic status of the USA was raised vis-à-vis all other combatants and participants in the war, which is to say that its economic status relative to all combatants was improved, but no one would rationally say that the cost of over 600,000 dead soldiers was “a good trade-off” for a relative improvement against some other countries.
In point of fact, the war cost the USA billions of dollars, much of which was expended in bombs and munitions overseas, lost ships, tanks, planes and other capital items, diverted production from peaceful enterprise, etc. ... and of course, the dead soldiers and civilians involved in the war effort, as well as the victims – both military and civilian – at the business end of the dropped bombs, artillery shells and bullets. And all of that was paid for – to the extent that it ever would be – by heavy increases in taxation of American citizens.
Which is not to say that there were zero economic benefits. The introduction of peaceful nuclear power stems from its use as the most horrific weapon of mass destruction yet developed, and in fact, the introduction (and limited proliferation) of nuclear weapons has so far prevented a repeat of that war. Again, rational holders of nuclear weapons do not want to expend or “use” them as other than threats.
And some people certainly did become rich from the production of war matieriél, but on balance “the USA” did not benefit directly in an economic sense. Of course, having the only continental land mass that was nearly devoid of conflict or wartime damage and the strong “relative” position of the US economy after the war enabled its production to switch fairly rapidly back to peaceful use after the war, without having to rebuild factories, bridges, roads and railroads, harbors and docks, etc. (that is “nearly all infrastructure”) after the war ended, but it can hardly be said that a nation “benefited from the war by not being bombed”. That’s a negative benefit if there ever was one.