^ Agreed. South Loop is very misleading in its density.
See the bottom of this blog post for an eyepopping illustration (Central Station has the same population density as some random 1950s bungalow belt area in Belmont Cragin). The reason this can be true is because of household sizes, South Loop has way more units per square mile but with fewer people in each one due to the relative lack of families.
https://chicagoflaneur.com/2016/06/2...ty-in-chicago/
That said, raw population density isn't the best metric to predict the success of a new mall. The people in South Loop probably have a lot of disposable income and are more likely to shop for luxury goods than the bungalow dwellers in Belmont Cragin. And South Loop is a tourism magnet, or at least tourism-adjacent due to the Museum Campus, Soldier Field and McCormick Place. Still, I think One Central has about 3x-4x the amount of retail that you could conceivably sustain there, and downtown retail is in shrinkage mode or treading water with the growth of e-commerce.