Genesis and John are not the same forms of literature. John is quasi-biography; Genesis is world history, not unlike reading Toynbee, with all kinds of theory thrown in. So what is literal in one is not literal in another.
Who says this? You? You get to determine waht is "quasi-biography" and what is "history with theories thrown in?" Is this what your "authoritative" church fathers taught, or what "we now know" thanks to nineteenth century German criticisism?
That being the case, why don't we apply a little nineteenth century German criticism to John 6 and I'm sure that you will see that it was meant to be taken "theologically," not literally.
Unless you are a hypocrite, of course.