Right! So, would you say a 10 kt fission bomb would kill millions in Manhattan, or 10s of thousands? Best guess.
Think if the WTC was still intact and a Hiroshima sized nuclear device was detonated in the middle of the complex ALL of the people in those buildings would have been dead(at the height of the work day 50,000+ in the north and south towers alone). I could easily see the total death toll from a 10-15KT blast in one of the more popular downtown Manhattan sites to be well over 100,000 in the initial blast and more than double that over the next week or two. IMO