I think I may share the same experience as you, but I've never known if what I have is closer to aphasia or hyperphantasia.

From the way people describe their experiences, it's difficult to know what they truly mean. I don't think anyone is lying, but it must be hard to convey these experiences with our language as it is.

In your first post, I thought "that's definitely not me", but in your second post I thought, "oh, that's actually 100% me"

To me, everything I imagine is on a different mental plane. This is what I thought people meant by a "minds eye". You don't see it literally, but it's there in your imagination.

What confuses me though is that for some people, it sounds like it's an overlay on their actual visual perception, something so vivid they could practically rotoscope it. I could never do that; I imagine I'd be a better artist if I could.

My imagination on this plane is so vivid that I'll get lost in it, and not see what's in front of me, as you describe it, simply because I'm "not paying attention" until some immediate danger jolts me "awake". I colloquially call this "zoning out" or "daydreaming"

Actually, I think my imagination might be part of what makes it so hard for me to read books. I'll get distracted by the world building, playing the different scenarios in my head, that I'll forget about the words in front of me, and minutes will go by before I remember I'm supposed to be reading a book.