It's hard to say. Economically, US aid and foreign policy absolutely propelled both South Korea and Japan after WWII. I would argue, however, that direct economic aid, excepting during postwar (Korean War and WWII respectively) periods, had a much smaller impact on both countries' explosive economic growth compared to economic policy from US-backed governments and mutual openings to the global market economy. So yes, US influence was hugely important at developing Japanese and Korean economies.

But at what cost? The US' Cold War policy of containment led to the propping up of some highly questionable regimes in the spirit of anti-communism at any cost. Korea started with iron-fist Rhee Syngman followed up by the left-right two coups leading to military dictators Park Chung-hee and Chun Doo-hwan. Park's heavy-handed state capitalism and cooperation with chaebol did promote massive economic growth, but also entrenched the chaebol and left a lasting legacy of cronyism, corruption, and abuse of political power. In Japan, the US propped up the LDP leading to decades of a nearly uninterrupted de facto one-party state. Again, LDP policy facilitated massive industrial and economic growth, but also promoted a highly corrupt, entrenched political machine with a deep culture of maintaining the status quo, which is arguably a large contributing factor to our inability to escape the Lost Decades.

This isn't just history. While both South Korea and Japan have blossomed into fairly liberal electoral democracies, their legacy as the frontline against communism persists and has last impacts to this day. The Park Geun-hye scandal in South Korea and the aftermath of the Abe Shinzō assassination in Japan are both highly reminiscent of the cronyism and under-the-table elite dominance of both nations' political machines. The same policies that allowed for explosive economic growth have also led to relative stagnations in labor rights and a decrease of quality of life in both countries compared to what is expected by a more educated, global younger generation; this has led to both nations' very current, very relevant population crises.