It's not difficult to understand
Correlation does not imply causation. In statistics, the phrase "correlation does not imply causation" refers to the inability to legitimately deduce a cause-and-effect relationship between two variables solely on the basis of an observed association or correlation between them.
Oh, but it actually does. Fe lead may "standardly" (implying correlation) fit to type 2, however there is no reason why an EIE especially couldn't be type 7 with their 4D Ne. Not only that but you'd have to take into account their other functions - for example, I'd say type 6 could be a good fit for an ESE as well as type 2. There may be correlations between descriptions of types in each system, but that is all. There will always be outliers.