I meant both. I know someone can always be typed but at a certain point through life experience most people develop their other functions that they don't use as well, this sometimes makes it harder to pinpoint their true type. Also I really think there are some people that use more functions more completely naturally, or at least come off as they do...and I don't think it's type related, but I do think some types are harder to recognize than others. I've heard before that ENFP is one of the types that is hardest to recognize for example. I think I agree with Jungian theory but I also think its just a theory rather than a strict rule that fits every person perfectly.
Well, as a rule, N-doms are mask wearers and game players. If you have a good working concept of everything you can seem like anything. That doesn't make them hard to type though, unless you only see them under one set of circumstances. They are hard to type only when they control the information they give. Not with reliable access to how they actually process information.
The thing, at least with MBTI, is that the structure and preference of functions seems arbitrary if you don't understand how they are supposed to be working together. Functions are not 8 isolated chunks of brain mass that shrink and grow independently.
For example, Ni collects information through Se. Fi collects information through Te. I actually imagine that these relationships are physical variations, meaning N/S and T/F respectively are probably cut from the same cloths. All parts of someone's personality need an external and internal component for them to function as a human being. Ni does not collect information through Si, for example, because you can't create information about the world from some isolated process that doesn't interact with it.
So the illusion of the isolated cognitive functions is a misunderstanding.
Yes, there's flexibility here... You could use a lot of Ni and very little Se, for example, or they could be more balanced. But the theory holds that you develop one function first, which essentially means that its counterpart will remain comparatively underdeveloped. That pattern seems true to the reality.
There's actually very little going on here. If Ni/Se is a thing, and Fi/Te, Ti/Fe and Si/Ne, then there are really only four building blocks to one's type, they just come in different ratios from person to person.
To simplify almost too far, if N/S and T/F are kindred, probably all MBTI is actually explaining is the proportion and localization of white vs grey matter.
And think about it, what would be the point of having equal function preference? People have limited brain matter, it doesn't vary THAT much. If you divide a person's specialty up four ways, you're creating four disjointed retardations. You have to specialize to be excellent, if we consider average human capability as excellent, and it is. So you get one dominant function with an underdeveloped counterpart, to get you in the door and functioning, and later you get a, I don't know, "backup dominant" or auxiliary function with its own counterpart to round out your personality so you can function as an adult who needs to at least get by in things they are not specialized to do.
That's my perspective, hope it's bot too vague and helps a little. Anyone should feel free to correct me if I'm wrong about any of this. It's just what I've strung together.