Both my wife and one of my co-workers experience hi-res images superimposed over their actual vision when prompted (and occasionally involuntarily). This opposite end of the spectrum is hyperphantasia[0]. There are accounts in this thread of people having trouble reading books because they're too caught up in the visuals the story creates in their head (something that same co-worker has also mentioned happening).
I just responded to you elsewhere assuming that you're operating from a baseline experience of depending on visualization, but this comment has made me think you might actually also lack it, and that your assertion that aphantasia must be debilitating is from an assumption that the lack we're describing is something beyond your experience. Since it's all a matter of your internal experience, though, it's impossible for me to know.
Indeed, I just wrote a sibling comment before I saw yours about the same phenomenon, hyperphantasia. I don't think that the parent is right that it's just "memories and concepts," it actually is vivid imagery for most people who don't have aphantasia. It does seem like the parent has some sort of aphantasia, just not as severe as seeing nothing, it seems to be more of a spectrum rather than a binary.
I just responded to you elsewhere assuming that you're operating from a baseline experience of depending on visualization, but this comment has made me think you might actually also lack it, and that your assertion that aphantasia must be debilitating is from an assumption that the lack we're describing is something beyond your experience. Since it's all a matter of your internal experience, though, it's impossible for me to know.
[0] https://en.wikipedia.org/wiki/Hyperphantasia