Bipolarity, while making classification relatively simple, just doesn't seem to be an accurate way of representing the issues. How many times, when considering type, are we asked to prefer a to b? And how often do we make conclusions on this a/b decision (or a small sample size of a/b decisions) when our "real" answers are more along the lines of "well, a is good in this situation, b in this other one, well, except if something else also happens, but when I was in a similar situation, I really didn't think a *or* b, or I thought *both*, or "*neither*. There really isn't one answer that's better in general, but I have to pick one, so I guess I pick a". For me, it's pretty often. Simplifying can sometimes give insight, but it can also sometimes discard the complexity that is absolutely integral to understanding - I think that's the case here.
Bipolarity just doesn't ring true for me, and I'd say that this goes double for introverted vs. extroverted functions. Not a fan of that theory at all, in that the "introverted" functions and the "extroverted" functions just don't seem to be dichotomous. A simplistic analogy is that it's like saying that liking oranges is opposite from liking broccoli, and that I have to have a preference for one over the other, and that this says something important about me. I just don't accept that the two are related in any significant way.