It’s a spectrum - most of us are ambiverts.
It has become pop psychology and never had much meaning.
This is not correct; they are not independent.
No, it isn't. The goal is for them to have high explanatory power. They aren't independent variables, and the fact that they aren't is a frequent criticism of them. But it's not relevant to whether they are useful descriptors or predictors.
Compare https://en.wikipedia.org/wiki/Big_Five_personality_traits#Li... :
> In many studies, the five factors are not fully orthogonal to one another; that is, the five factors are not independent. Orthogonality is viewed as desirable by some researchers because it minimizes redundancy between the dimensions.
It was developed by people fully aware of what orthogonality is, and understanding of why orthogonality is desirable. The fact that it is not perfect is indicative of the complexity of psychology and the bluntness of our tools. There is no system that is more orthogonal that explains near as much (I qualify it that way because dead vs alive is simple and pure but of little explanatory power).
We have nothing better than the Big Five (there are proposed refinements but they are not yet generally accepted), and it is better than what came before. The Big Five separates variables that used to be mixed, and can't yet explain the unexplained, but neither can any other system.
Unless you think that "these five variables appear to be independent when measured" conflicts with "these five variables are not independent".
It doesn't seem like that tricky of a question, but maybe I'm missing something.
Given how obviously true it _appears_ to be when talking to people about their experiences, why do you say that?
Interestingly, I know people who say they are socially anxious extroverts—they need to be with people to draw energy but have high levels social anxiety. This usually means they need to spend a lot of time with people they know well and trust.
My new favourite word!