Arguing that something isn't a spectrum and then immediately comparing it to something with a clinical name that literally has the word "spectrum" in it really isn't doing yourself any favors.
I don’t know much about it, but a source used by Wikipedia says:
“It is also possible for a non-disjunction to happen after fertilization (about a 1-2% chance). In this case, some of the patient's cells are normal and some contain the extra chromosome. This is called mosaicism. Patients with this type of Down syndrome have milder symptoms.”
I often cannot recognize people I know mildly well, especially if I lack context clues. This is not due to carelessness: trying harder does not help. But I do not have complete face-blindness.
Whether this means that you are wrong about when prosopagnosia is a continuum, or whether it means we should characterize how things work for me in terms separate from prosopagnosia (and thus perhaps in terms separate from face-blindness), I do not think it is productive for you to basically insult me and everyone like me by attributing our behavior to not trying hard enough. I've tried quite hard.
It's very socially bad not to be able to recognize people. I pay high costs for this inability and I would love to eliminate it if I could. I think (as the OP suggests) being aphantasiac might make it difficult for me to remedy this inability, because having a visual memory might be the best (the only?) way to record features of faces well enough to recognize people you know mildly well. I am aphantasiac and that too is something I cannot remedy. I would appreciate not being lumped in with assholes.
