Not a definitive, but bearing in mind the Max was re-engined (possible weight increase?) together with the increased torsional load at max power from these donks, (think Thrust x Distance from the donk thrust line to the centre of torsion of the wing structure), one would expect the pickle fork design will have been beefed up to cope with these additional stresses. This considers the static case.

There may may have also been different dynamic/vibrational characteristics (mindful that aeroelastic flutter has much to do with the coupling of torsional and bending characteristics of the structure) which may have resulted in an increase In the beefiness of the structure.

Changing something as simple as a winglet can have a massive impact on the torsional and bending loads placed on the root of the wing, as the pressure distribution is significantly changed.

beefed up in relation to increased loads. What is frustrating with airframe structures is the difficulty of protecting structure from cyclic stresses (dynamic case) which are more difficult to model. You could build the structure up significantly but still come up against high cycle fatigue if there is a vibrational mode that you haven’t modelled correctly. Aeroelastics are another significant complication (together with Aeroservoelastics) which are rarely encountered in other engineering fields. The compromises to provide economically competitive structures vs aircraft with a reliable long term structural integrity are as old as aviation. This issue has been spotted now and something is being done about it, which is the key differentiator between this and the MCAS issues.