The CORE system design uses a single set of fasteners across two sets of bosses on two planes. This design means cumulative tolerance stacking occurs across the slide to plate interface and the plate to optic interface. In my experience, this is the major practical problem with the CORE design. Unless each of the optic, the optic plate and slide cut mate up tightly as a unit, the effectiveness of recoil bosses is compromised and proportionally more force is transferred via the optic screws. Regardless of how tight S&W executes their slide cuts, in practice optic plates have looser tolerances and optic tolerances are all over the map depending on the manufacturer and model.
The MOS and most other mounting systems use a separate set of fasteners and recoil bosses on each interface between planes. This design limits cumulative tolerance stacking across interfaces and in practice means plate manufactures can make their optic to plate and plate to slide interfaces tighter because they don't have to worry about a slight misfit on one interface compromising the fit on the other interface.
This may also contribute to the divergent experiences with the CORE system. A particular model of optic on a particular manufacture's plates against a particular run of M&P CORE pistols may work extremely well. Changing any one of these variables could result in a different experience.