[bstnbstn]

> Also, it is near impossible to report objectively about your inner processes in a useful way.

There are some objective ways to measure visual imagination, for example binocular rivalry, skin conductance response (influence of imagery on emotions) and pupil responses during visualisation. Differences can be seen in fMRI. Also, the VVIQ (Vividness Of Visual Imagery Questionnaire) is considered statistically reliable.

> It may well be that some people actually have some form of aphantasia, but all the self reporting of amazing visual powers or the lack thereof seems more indicative of peoples' egos than the actual differences in what they are capable of.

Over 10% of people are hyperphantasic (“Phantasia – The psychological significance of lifelong visual imagery vividness extremes”), and the average visual vividness is quite high.

I guess especially in the Internet you find more people from the extreme ranges of the spectrum who search actively about the topic. But whether someone rates himself with 4 or 5 (simplified) does not have much significance individually anyway.