> I have always suspected that people with “aphantasia” simply misunderstand the idea of a “mind’s eye,” believing that others can somehow visualize something in their actual field of vision at will.

Many people can do precisely this, though the projected image is not usually 100% clear in some form, i.e. it may have a translucence or impermanence, and it can indeed take some practice to develop this skill. But it isn't uncommon at all, and comes up regularly in some spiritual and meditation practices.