There's some pretty good points in this thread and i also like the idea about the +/- 3% production values tolerance. I was about to propose something similar but i thought it would infuriate too many people so i didn't
In any case, i think the general consensus is that we do need accurate FMs but as in real life, the FM should not be super-consistent each and every time between a bunch of different airframes (at least when a relevant difficulty/realism setting is enabled).
If we could combine that with a dynamic campaign engine in the future (both for single and multiplayer) to track the condition of the aircraft between sorties and provide some continuity of airframe, it would be very much closer to how things used to be in reality.