"One thing I have noticed is that many Ts find it especially hard to admit to having irrational motivations and claim to be totally objective and rational when in actuality they are rationalizing said irrational motivations. Point out the rationalization and they will instinctively get defensive because you are threatening the essence of their ego-image ("I am rational, I am logical, I am intelligent")."
I have experienced this EXACT pitfall in the T placement, but I believe this tendency is mitigated by character and environment and can be "momentary" for some, versus a continuous defense mechanism in others.
For myself, I am a slightly expressed F, but almost 100% N. So an N placement is more important in any kind of relationship I seek, otherwise we seem not to be speaking the same language (though differences can be fascinating, yadayada). Which means an NT has a great chance with me, verus an ST.
In my last professional position, I reported to three T's - An ESTP, ENTJ and finally an ESTJ.
All were dominant males in competition with each other, predictably! boyz. All intelligent and quite temperamental (in their own minds always "logical" despite erratic screaming, red-faced fits - in the workplace. not kidding). Per their conversation, it was other people who were "soft", "weak", or "personalized everything". When this view came up in conversation with any of them, I gently tried to ask them why they thought this or to describe an interaction with another person that could by definition not be "personal" and usually got blank stares or a litany of 'impersonal" subjects - they failed to answer the question, ultimately. And it is not that there couldn't be an answer, but since they skirted the question I assumed the actual answer might go something like this: "subjective assessments are crap and for the weak. I am smart and not weak. Your focus is flawed and therefore not worth responding to, end of story."
I had the most "success" with the ENTJ interpersonally, he at least expressed interest in my assessments, but he was confused by my approach, culiminating in an "I just don't understand you" moment before handing me off to the ESTJ (yikes). The NT told me once that he thought I was bright and always seemed to get to the core of a situation but he did not know how I did it. I thought this was very honest (typical T). His "skills" were on a different plane than mine, actually, but he was intimidated by navigating people's emotional responses/non-rational factors so he opted to ignore them or make fun of them. Consequently, he surrounded himself with particularly immature T's who nodded in agreement with him either because they agreed, or for their own, strategic reasons. And he frequently got the wrong answer when he attempted to analyze why something was occurring in the business- not a pretty result for an ENTJ.
The worst obstacle I found was with the ESTP, but so much of this was centered around extreme ego and character issues it is hard to tell who he would have been absent these problems. Every failed result he was involved in was explained away by the other's low intelligence, to the point where he was describing most of the people he worked with (how likely is that at an engineering firm??). My aproach with him was to repeat that he was lucky to be gifted, but unfair and unrealistic in his expectation that others would be on his level, and also incorrect that some weren't. I knew for a fact that several folks literally avoided him to protect themselves from his condescension, pure and simple. Some very bright, but sensitive people.
A final word on a T placement. I enjoy T's, even more so than a very strong F, yet all of my close friends (and my partner) are F's or X's. Personally, I am not threatened by debate and have been delightfully cornered many times in conversation with a T. They certainly have emotions and relate to people emotionally, as everyone does, but subjective understanding is not their filter or first, surface approach, and this is fine, in fact useful. Always funny to be busted on idealizing, ignoring "facts" that contradict my goals, and so forth. I find them to be more sentimental and vulnerable when they aren't in touch with themselves, and as an F, this makes me sympathize with them and see this position as a disadvantage. I once read that a T risks being manipulated via their ratonal attitudes, and I have seen this.
But. When they use this deficit to mistreat others or emotionally "abuse" people they are responsible for, my sympathy dies and I move into a J mode - you reap what you sow. They can be come quite isolated, but in this sense, by their own hand.
A final, final thought. One ENTJ whispered the following to me at a gathering, this is regarding a female subordinate of his. "I said 'hello" to her and she blew me off! She just ran away. Can you believe that?". My response? "Of course. She is afraid of you. Why would anyone be responsive to friendliness from someone they fear?". And I walked away, leaving him puzzled.
So is T "rational"? Not necessarily. Critical thinking and evaluation requires the ability to recognize and synthesize information, including "mysterious" equations like mean=avoidance. Can they be attractive, valuable and "true" friends spouses for an F? Can they love and respect differences? Why not! Definitely.
Can an F do the same for a T? Yes, but the F may struggle more than the T and the struggle may or may not be worth it. Some interactions require so much work that they move beyond the dynamic to the pointless.