This is fairly conclusively disproven by far more than just fMRI / brain-imaging studies. E.g. aphantasics have problem with visual memory recall, visual priming, pupil dilatory and skin conductance responses when imagining light and/or fearful stimuli, and many other results (especially acquired aphantasia) that don't depend on brain imaging and obviously rule out semantic explanations. Likewise, rejecting the reality of the phenomenon also seems to require believing an extraordinary amount of error and/or conspiracy on the part of highly educated and insightful people that explicitly are saying the issue is not one of semantics / description. This is also not to mention the rich history of visualization practices in much of the worlds religions and esoteric practices (which make basically zero sense if this is all metaphor). See e.g. the discussion in a previous HN thread (https://news.ycombinator.com/item?id=49464414).
> I invite you to feed your own friendly AI these references then ask it to analyze the recent papers [...]
Likewise, an unbiased AI prompt (or two prompts in separate sessions, with opposite biases) will clearly reveal the "semantics denialist" case has very little to stand on here. Yes, there are communication and linguistic issues, but these only cover a subset of ambiguous cases. Rejecting or denying the reality of aphantasia is an extremely strong indicator you are aphantasic, to some considerable degree.