Why use a proxy, when you have access to the real deal.
Because I like categorizing the real-deal.
/Half Tongue-In-Cheek
I see MBTI has a means to communicate; a vocabulary.
But in all seriousness, I agree with Sytpg. MBTI is merely a communication form, a set of tools, yet not the
only available set. It just contains the most useful tools I've personally encountered. I rely less on type than I do on functions. And I almost neglect any arbitrary category like gender, race, class, sexual-orientation, etc. These labels are important to the rest of the world, but they do little in persuading me to change my mind.
For example -- knowing that someone has Fe in the auxiliary or dominant position is very helpful for me because it's the one Je function I instinctively rebel against. "I need to respectfully value each living person" isn't enough for me to stop Te-ing the daylights out of that individual, because I think to myself --- I can do it, so why can't they? Or sometimes the situations are reversed and I'm left confused at the difficulty I have in doing what appears to be natural for other people.
And MBTI/Jung rectifies that. I understand what's blocking them from doing certain things, and how they can get around it. I intellectually recognize that "Wow, people are very, very different from me."
So MBTI/Jung is what you make of it. Either that can limit your perspective, or broaden your horizons. This is your choice.
But I truly think it's naive to assume that without MBTI, people don't try to organize the "real deal" in some "me vs. you", "us vs. them", "mind vs. heart", etc. form. It's how we differentiate our surroundings. That's why we have theories to generally explain odd phenomenons, invented counting units like math & time, rally under groups that share our beliefs, and so on. If they are not relevant to what you seek, then throw it out. Yet, however, this alone doesn't take away the utility it has for someone else.
As another example, math is practically the mother language in physics. But in something completely messy, imperfect and subjective like relationships? It's as useful as the neighborhood troll. MBTI/Jung can be the same way. Their usefulness depends on how, why, when, where, what and who it is used for.