Dunno Arty it seems to go deeper than just pilots and navs. The last guy I heard giving the J a going over was a senior officer pilot (albeit currently flying a desk).
It just seems to be the place - wierd mate.
Most Herc threads on here of the last couple of years always degenerate into a K vs J bunfight and a "my seat is better than yours". Interestingly the only guys who seem to keep out of it are the Engs - having no experience of flying with such chaps I am not the one to draw any conlusions from this!
Think on balance I would still rather fly with a good nav than a co, not that I am greedy of course!