My two cents: I think putting people in "A" or "B" groups wrt personality disordered traits goes against the idea of a spectrum, which implies a distribution along the expanse from "no traits" to "severe impairment"... .
The premise of the question requires categorisation under 2 groupings (High/Low or A/B)
Classification doesn't invalidate spectrum distribution, it merely indicates segmentation of the spectrum. (You actually provided a sample segmentation in your example [None/Severe])
and also I don't think the expressions of disorder can be sorted into high and low functioning, exactly.
Not sure if you misinterpreted, but I agree but the expressions of the disorder aren't being classified, the traits are (tho admittedly extremely bluntly).
I agree with you that a spectrum of BPD doesn't make much sense anyway.
A spectrum of disorder may, particularly due to comorbidity. I've been trying to research medical/clinical opinions recently, and there seem to be surprisingly few professionals so far who do not believe BPD/NPD are always co-morbid to some extent.
For instance, is it necessarily true that someone who is less impaired would be more impulsive, infjEpic? I don't think so... .but I am not an expert.
Again, not sure if you wrote that incorrectly or misinterpreted.
In the example I outlined above, Group A are low functioning. So someone who is less impaired is more impulsive, not less. Personality disorders manifest in a social context, hence they struggle with the broad range of social contexts.
High functioning, by it's very name would indicate less impulsivity - (or more self control, in general, but not in entirety). As an example, they can be highly successful in their career or other social contexts, they have substitute coping mechanism and only family members or intimate partners may ever experience their disordered behaviour.
It's important to stress here - I'm not a professional, and there is no medical or scientific fact in the opinion I've provided.
This is merely the current impression I've acquired through reading