New York is definitely a world-class city, but Amazon had the opportunity to attract talent to make a city that is not currently a world-class city into one but instead selected an already established one
Not really. Big cities operate at scales and complexities far above what Amazon can bring. Density begets density. Meanwhile, that cities have largely been built—and remained—in similar places (protected harbours with navigable rivers and ideally shallow bedrock) implies there are deeper reasons for why density exists where it does.