Japan and Korea never were an equal rival to USA. Never near to replace it as Number one.
Korea is "small potatoe".
Japan has third of population and never was near to surpase USA in GDP. Japanese GDP is 1/3 of USA. South Korea has 1,5 trillion $ while USA is 19 trillion $. Source:
https://tradingeconomics.com/
While their growth was significant, Japanese main gdp growth was in overpriced property buble (1985-1995), not in exports.
Japan NEVER had continued GDP rise od 10 $ for period of 25 years !
Look at this table which shows massive oscilations between 12 and 4 percente, on average about 6. And this is after 15 years of slow and steady investments in aid, infrastructure and factories, with US Army taking on burden of defence.
Japan did not make it alone. US assistance totaled about US$1.9 billion during the occupation, or about 15% of the nation's imports and 4% of GNP in that period. About 59% of this aid was in the form of food, 15% in industrial materials, and 12% in transportation equipment.
Let se. Military dictatorship from 1945-1951, followed by limited soveregnity under one party rule (Liberal Democratic Party), with no female equality, does not sound like a much better alternative. Korea was also a dictatorship untill 1980. Even today smaller than France or Canada.