@ChuChu
No, you are quite right, MZFW is simply a means of limiting the weight in the fuselage.
I am not sure what you meant by fuel close inboard, but any fuel loaded outboard of the wing root fixings will contribute bending moment relief.
Discussion of the effect of fuel loaded into a centre tank is a bit of a red herring, since so far as wing bending moment is concerned there is no difference between a pound of fuel in a fuselage tank and a pound of payload carried in the fuselage. Besides which, there are a lot of airplanes out there that do not have centre tanks but they all nave MZFW limits.
As I wrote previously, the wing design bending moment is usually 2.5g at MTOW, but that should strictly be modified to read the combination of payload and fuel (no centre tank) that gives the highest wing loads.
So you could theoretically have an aircraft with a high MZfW and a low fuel tankage where at MTOW the wing bending moment was bigger than the same aircraft with the same MTOW but a lower payload and more fuel.
However, this would NOT result in overstressing the wings because if it is a permissible loading case then the design must be shown to be capable of withstanding the loads. This is true even if the TOW in this loading case is less than MTOW.
And again, MZFW is not necessarily set by wing bending