problem is... most of the non-mil pilots under 35/40 have never flown an non EFIS jet...
One of these pilots flying without FMS is like a baby without a dummy.
I reckon some Company MEL's don't permit dual FMC failure (assuming FQIS functioning of course) because the poor darlings wouldn't have a clue what to do.
And before you start flaming - I hold a 733 rating. So I'm at least au fait with the situation.
toodly doo