I think it's weird to call an aspect of mental functioning a pathology simply because it's not the majority, regardless of any impairment in normal functioning. Depending on how you slice definitions many many things are in the minority.

Those studies, well, I'd have to see them. There's the risk that people for whom (e.g.) memory is accompanied by imagery automatically assume that imagery is required for memory. Vague correlations with social functioning can be drawn for nearly anything.

Regarding dementia: obviously the disappearance of imagery in someone who used to have it is very different from someone who never had it.