Your statement could be true for Quant, but not true for CB. Columbia has professors from Baruch and UCLA: Keith Todd Wilcox | Columbia Business School Directory My ranking is for 3 tracks not only for Quant.
USC has placement at MIT, Chicago, Michigan even in finance, more heavily quantitative:PhD Program | USC Marshall
even for Quant Marketing, Harvard has Prof from Pittsburgh Rohit Deshpande
- Faculty & Research - Harvard Business School.
Stanford has 2 Prof from Duke, 2 from Ohio state in CB track.