BPDs are "extreme followers" which seek whole systems of validation, identity and meaning from their local social environment. NPDs are "extreme leaders" which cannot receive this validation socially, so push-out a delusional theory of their own identity (, role, value system, etc.). -- Which is why, so often, the structure of a cult is one NPD leader and a coterie of BPD followers.
If this scale exists, ie., from follower-to-leader... then many conditions can influence your position on it. A "healthy" person is presumably one who, I'd say, is mostly a mild follower but will adopt a mild leader position when required (eg., by role).
In ASD, my guess is that since some social mirror / double-empathy /etc. is different/impair, you get NPD-like problems because you're not getting that social validation feedback signal, so you're having to push out some validation/identity/etc. system of your own.
Likewise in ADHD, you tend to find a lot of social rejection due to impulsive behaviours that alienate people.. so you get a comorbid BPD-ish quality where you're aware of the social validation available, but are constantly fighting your own impulsive undermining of receiving it.
One diagnostic difference between the ASD-ADHD vs. NPD-BDP categorisation should be the possibility of self-awareness, where in the former you'd expect improving self-awareness to have some immediate benefits -- but in the later, often none. Since position on the leader-follower line in ASD/ADHD is effectively an "ecological concequence" of repeated accidental behaviours, whereas in NPD/BPD its something stranger and I think less well understood. One imagines, most probably, very early infant trauma that has severely impaired psycho-social development.