then it is still within its designed limits and therefor should theoretically be as safe as the realistic example
.. not necessarily so. There are two "strengths" to consider -
(a) static - this is what the normal G-loads relate to and prescribes an isolated requirement for the structure to withstand the proof load without any failure and the ultimate load without any catastrophic failure
(b) fatigue - this is a reference to the structural bucket of strength. One makes a withdrawal as one flies .. and the harder one flies, the bigger the withdrawal each time. The OEM makes reasonable presumptions as to the sort of flying the Type will do and does the sums and tests accordingly. Although there is a fair fudge factor in the figures, if Captain Pilot routinely does unexpected things .. then Captain Pilot's specific aircraft might find itself with an empty fatigue bucket of money earlier than expected and face the prospect of a premature significant failure .. not good.
So, while MZFW and the other limits are based on maximum loads, that is only part of the story. One is presumed to fly appropriately.
Occasionally, an operator will seek the OEM's revision of fatigue analysis and certification lives based on a review of the specific operation. Indeed, some OEMs prescribe multiple lives depending on the sort of operation conducted.