take me for instance: i am dominant N, but my auxiliary and tertiary functions are aligned towards neither ENTP or ENFP, because i use both Ti and Fi. i place myself in the middle because Ti and Fi are competing against each other; and so, i am ENTP 50% of the time and ENFP 50% of the time. there are probably many more on this board whose function priorities are different than their listed type, however little they want to admit it.
there's much more to this, but it would require a seminar to explain all of it. in due time, i'll have to write a book. anyway, enough of my theories.
preference is always a limitation, as it is a definition. if you want raw unlimited power, you cannot define it, and thus you cannot use it. if we didn't define the processes in our heads, we'd just have one big process and consider everyone equal in their mindset. however, this would not be very accurate. so we sacrifice some of that power to create limits that we can use to understand and research differences in mindsets. 16 MBTI types are better than 1 type, since they would be able to more accurately pinpoint differences between them.
the reason why i see S/N as the greatest gap between types is because how i have seen S and N people act. there is a reason why i consider S people unable to do some things that N people can do, and vice versa. while you may want it to be different, there are limits for both parts - if there weren't we wouldn't have 16 or 100 or 1000 types, we'd just have 1 type and just use that.
i have seen what spielberg has done and how he has done it. i have correlated it to some of the things other Ns have done (including myself), and i have concluded that he shows thinking with intuition; with his messages in movies, his way of directing. i see no sign of S in this, because S wouldn't be concerned with the messages behind the movies. S wouldn't be concerned with meanings or messages between the lines; S would be concerned with what is up front. and while spielberg has directed action movies, even there he shows ability to go beyond just what happens on screen. if this isn't the definite proof that he is N, then i don't know what is.
but - if you are so sure he is ISFP, then tell me this: could you see yourself making the same movies he has done, in the same way? could you elevate something from just being a movie to something much greater? i know i could; and if i was making movies i would come very close to some of the things he has done.