>People who don't have aphantasia see objects in their visual field, occluding reality? That sounds like hallucination, and very unsafe unless you have a high degree of control over it. An imaginary horse pops into your visual field while you're making a tricky maneuver on the highway...
Does the image from your left eye occlude the image from your right eye? No, it doesn't.
It's the same for mental imagery. It's a third "image buffer", alongside the two from the eyes. It coexists in the same coordinate system as the other two, but it doesn't occlude them.
Can you imagine a song in your head? If so, does it drown out the sound of the real world? Again, no.