Have you ran any tests? Like I said, theoretically, MM is way better. But somehow lvl 50 sets are still outpreforming it in time taken to clear a map solo with several constants in place to ensure validity. The only thing I can come to on why it is being outperformed is how much of a gap there is in hit and crit.
But again, like I said, I am testing only one component of MM, its ability to clear maps. I would still use MM over shadow and the keeper set any day for its other attributes.