You’re really stretching with the 1997 comment but you’re technically correct so I apologize for saying that NU has never been in the top 10. Of course NU has some departments that are ranked higher. It’s a great school. I’m not trying to give the OP the impression that Duke is Harvard and NU is Kansas State!
Also, Duke’s endowment per student (the statistic I’d argue matters more) is higher but you’re correct about the size of the overall endowment.
Moreover, the OP is probably interested in leveraging his economics degree to get a job and Duke graduates make significantly more money than NU grads ($76,700 vs $64,100) according to the government’s college scorecard.
https://collegescorecard.ed.gov/school/?198419-Duke-University
https://collegescorecard.ed.gov/school/?147767-Northwestern-University
It’s probably also worth pointing out that 89% of students who have admitted to both schools choose Duke.
I agree with your final comment. The OP isn’t going to be at a significant disadvantage if he attends Duke over NU or vice versa.