To me the phrase "MBTI is a system" explained it all, cause systems dont work with people. The most basic example in that regards is trieing to define a person that has no mental illnesses or a "normal" person.
A student of psychology once told me there are two ways to deal with knowledge concerning the human psyche. The first is you become an engineer of perfection, who seeks out every single flaw he ever learned about in the human psyche and generates role model understandings or systems to explain to himself why people are doing things, what their motivations are.
The other type of psychologist is the more relaxed, reflective one. He has accepted that people have flaws and will never fit any system, therefore he tries to give them examples from his own experience or the experience he learned through his studies.
One may argue now, who has the better approach.
Back in the days C.G. Jung made his archetypes, he used the same tools as the nazis. Meaning the nazis had their own typology system, which did analyze and categorize people like that and Jung tried to present them with a more colourful, versatile onlook on the human psyche. To show them people aint made for war only. This was a very brave attempt, nevertheless if you look at his archetypes nowadays, it uses the same analyzing and categorizing methods like the nazis.
To me mbti didnt bring much harm. It really helped me to gain a better understanding of my surroundings and to understand their motivations better. But when I had really fun with it, I overdid it to some extent. My overdoing was i.e. I couldnt decide what type I am. And in the end I asked myself, what for, I can be all types. And nowadays I choosed entp because it fits my nickname.
And that's basically what I wanted to say: if you can use mbti as a way to get in better contact with your surroundings, it helped you. But then you have to stop and not overuse it, if you are not a big fan of over overanalyzing people and rather take them as they are. Any other approach can lead you trieing to change people for the better, cause you think they for example dont behave very intp like in that special moment.
In Europe mbti is considered wrong in the therapists world. And dont ask me for more info on that, I am no therapist nor a big speaker.
Another fact is, the base of all scientific research is to question estblished truths over and over and over again. Therefore I wouldnt call it Fi doom-mongering.
Another thing is, I am a bit sad about people teaming up and collectively attack the op starter for not following general consensus. That is, sorry guys, a very american thing. I hope you may learn some day that there are never wrong questions, just dumb answers.