According to conventional wisdom- Kellogg attracts student who have stronger soft skills and are more sociable while Chicago draws students with stronger quant and technical skills but weaker social skills. There might be a kernel of truth to this but there are so many counterexamples that I would not take the conventional wisdom too seriously.
I suppose "uptight" can have a variety of meanings. Chicago is certainly a serious place and a school that prides itself in the notion that ideas matter. However, it has the social aspect that one would expect from the typical high cluster MBA program as well.
Regarding the lack of preparation for executive positions of Kellogg students, I would not consider this a major concern. Northwestern is clearly one of the leading schools in the training of general managers and many of its students remain in Chicago. Of course, one would expect some Kellogg alumni to be poorly suited for executive positions but one would expect the same of the alumni of any major school including Chicago.