Hmmmmmm.
It needs a lengthy essay to respond to that properly.
Vision, as in the sensory process, whereby external light signals are converted into internal imagery and can be stored for future reference.
Imagination, as in the internal fantasy reconstruction of acquired and stored sensory information.
The former as in an immediate process relative to an optical system that under normal circumstances cannot be expanded upon.
The latter as in a contrived process only limited by the potential of the brain and the potential of stored information.
They are not really competing processes, one just facilitates the other.
Though without an optical sensory system, there would be no relevant internal information.
Interestingly I seemingly do not process aural information in the same way...That is to say I do not imagine fantasy tunes or noises...Do you?
Maybe this is the difference between myself and a gifted musician.