LOL, Ok.
City proper is pretty meaningless and irrelevant in an increasingly metropolitan world, but in any case Seoul isn’t that big. City proper of Seoul has about 10.3 million. New York is approaching 9,000,000.
According to Wikipedia Seoul’s metro has grown to over 25,000,000 with New York at 24,000,000. Seoul’s slightly bigger but not anywhere near 3 times bigger.
They’re both REALLY BIG.
Compare crime rates if you really want a shock.