Hence "mostly." But if you look at the full Myers-Briggs summary, it slots people into one of 16 categories and then has a nice little writeup describing people in that category. Which is a long way past acknowledging that some people are more comfortable dealing with abstract mental models than others or that some people want to deal with facts over emotions.

The actual science, such as it is, is also rooted into Jungian psychology which doesn't really have a lot of actual science behind it.