What happens if type is only four preferences? There are only four functions, to separate them by how they are preferred to be employed is to cross pollinate two facets which would erroneously leave you with eight elements.
As for some types being diplomatic and other's not being diplomatic... I think you're either too strict in your definitions or missing something my friend. ENFJ's can be diplomatic and are MUCH better reads on the state of people than INTJs can be. An INTJ friend of mine upset an ENFJ friend and when the latter pretty much snapped at him and stomped out of the room the INTJs response was "Was he upset?.... At me????". Ok so my response as an INTP to laugh and roll around on the floor wasn't diplomatic in the usual sense but it got them talking to each other as they discussed which should kick me first