I have not had time to read every page of this thread, but I will still venture a few remarks, based upon the most recent exchange.
1. If I recall Jung correctly, he considered both thinking and feeling to be rational functions. In any case, since everyone uses every function, at least to some degree, F and T cannot be mutually exclusive.
2. Someone (Mycroft?) wrote: "reason is the faculty concerned with objective phenomenon and, consequently, the only method available to us to arrive at any truthful conclusions about reality, as it is presented to us." Reason might suffice to explain everything if reality is entirely objective. If one admits that reality has a subjective component as well, then a subjective yet rational function would be suited to addressing it.
3. As an example, consider someone who loves you: your mother, your SO, your best friend. How do you know that they love you? Can it be proven objectively? Their observable behavior might be consistent with a loving attitude, but might it be possible that they have ulterior motives, and are merely acting in such a way as to make you think that they love you? The whole question is subjective, but it is also important. Relationships are a very real part of our daily lives, and we must make decisions based on the subjective evidence of such situations, knowing that we might be wrong. But objectively reasoned conclusions can be wrong, too, since the soundness of the conclusion depends upon the accuracy of the underlying facts, and we often have incomplete or incorrect facts. Even scientific principles are never really proven; if not disproven, they are simply supported.