Enneagram (and MBPI before it, wildly popular in the previous milleneum) is not a very good predictive tool. Big-5 remains the best scalable predictive framing, especially when combined with IQ (or a proxy).
Enneagram may be WAY better for reflective and support uses - a guide for how to understand oneself and one's preferences/choices, and to some extent what default communication and coordination mechanisms are likely to fit well (to be adjusted in actual relationships, it just provides a starting point).
There's no possible small-dimensional model that's going to be very good at showing the diversity that exists among humans, or even among culturally-similar humans.
We all know the typical mind fallacy—the bias where we assume that other people’s minds are much like our own. It happens because most of our evidence for what minds are like comes from experiencing what our own mind is like, and thus we infer from that evidence that the minds of others are not so different from ours.
The typical mind fallacy is deep-rooted and hard to change, since it’s difficult to get good evidence about what it’s really like inside other people’s heads. Even when we try, we inevitably parse the evidence through the lens of our mind’s understanding, and so may easily misunderstand when we think we’re really getting it. We can’t easily escape the “bias” that is the entirety of our lived experience, and so though we may learn theories about how other minds work, our understanding of them remains grounded in intuitions gleaned from observing just our own.
If you study the psychology of personality, it can feel like you understand that other minds are different. You learn that some people are introverted while others are extraverted. Some are more conscientious or neurotic or judgemental or open to new experiences while others are just the opposite. But in many ways, these are surface level traits of minds because many of them are surprisingly mutable. We can apply interventions like psychedelics to increase openness, meditation to decrease neuroticism, and cognitive behavioral therapy to increase extraversion.
The theory of personality traits makes it seem like people are different, but not fundamentally different. In effect it says minds are like ice cream, and personality traits are flavors. Some people are vanilla or chocolate or strawberry, others are rocky road or Cherry Garcia, but in the end they’re all ice cream, and not really that different when you get past whatever has been mixed into them.
And to be fair, minds are not totally different. There are large commonalities among the minds of all humans, mammals, and even all chordates. And yet, as it is said, mind design space is wide. Even within humans it is surprisingly wide. This just isn’t obvious because typical mind bias and distractions like standard personality theories give the impression that other minds are merely slight variations on ours.
But I’ve come to believe human minds can be quite different from one another—less like different flavors of ice cream, and more like different kinds of dessert. Only, I couldn’t see this for a long time because I didn’t have the gears to make sense of it. Luckily, I think I have found some gears, however fake they may be, in the Enneagram.
Much of the Enneagram’s value is that it aims to explain the core generators of our behavior, which necessarily means explaining how different people can have different core generators. Or, even if the generative processes turn out to be the same, it explains how the initial inputs those processes are given produce people who think and behave in wildly different ways.
It suggests that we have what it calls a core “essence”, but what I might describe as a strong, inborn prior. So strong that it’s woven into the structure of our brain and body in a way that makes it immutable without turning us into a different person. This prior sets the stage for how we approach life, determines much about what we most deeply desire, and causes fairly predictable patterns of behavior that fit into a system of types.
The Enneagram says there are 9 or 27 or more of these types. Another system might give another number. But the value is in seeing that the Enneagram isn’t just another personality theory like MBTI or Big5. Instead, it’s an attempt to show us what is in our “souls”, and once you see that no two “souls” are exactly alike, and you have a theory of the mechanics for how different “souls” make different people, it’s hard to make the mistake of believing that your own mind is typical, let alone anyone else’s.
Even if you can’t use the Enneagram to predict how people will behave with perfect accuracy—though I do think if you learn it well it can improve your predictions!—it’s a theory that has value in humbling us to the vast differences in human mind space.