No, that's just silly. In fact, it is precisely the point of such historicizing that such overarching conceptual frameworks DO change over time, and indeed may always be in the process of changing. Yes, and this sort of reasoning is specious. My impression is that Crossan does this, though perhaps not as much as some would like. No, it's a question of using hyperbole to reflect what I've read on the oral-written divide.
Modern memories can be just as prodigious.
Sorry, I think you are assuming the wrong book. Yeah, you already noted this. As I've pointed out before, I've memorized HUGE blocks of material, rather easily, in spite of being a literate person. That in itself an excellent motivation to maintain the tradition. And again I would suggest that this in itself does not much support the claim that the gospels are not literarily related.