It's such a load of old shite.
Human beings are intrinsically similar to each other, whilst also being utterly unique. It's why Derren Brown is so good at what he does. We are predictable creatures with a mixture of limited traits. It's the combination which is of interest I suppose. But it's like the lottery. There are only ever 49 numbers for example, but chances of nailing down the six that will be selected in advance, impossible. Still only 49 numbers. But we ascribe patterns to them, pick meaningful numbers etc, describe certain combinations as special.
Additionally, a lot of people I know are shit at recognising their own traits (me too probably) and claim all sorts about where they sit on spectrums of personality and belief when everybody else would describe them completely differently.
Similarly, people seem to think introvert = likes staying in with a good book and extrovert = likes parties and noise and it really isn't that simple.
People do like to find boxes in which to sit though. It's why it's wildly popular with teens, same as astrology. They want to understand themselves and the world. Nowt wrong with that I suppose. Most people grow out of a love of Myers Brigg, as you'd expect as they mature.
There's always a "rare, special" personality type, have you noticed? Like Indigo children. Or people who describe themselves as empaths. My mate who is a psychologist reckons the only universal trait is that everybody believes they're a bit different or special. And she says if you verbalise it, the other person will always protest they're not like that. So actually different and special because they don't think they're different and special. Like a worm eating itself...