Well, Mienshao actually has an advantage over Terrakion: Regenerator. Unlike Terrakion, who cannot keep switching in and out, Mienshao has the perfect combination with U-Turn + Regenerator to make it a good scarfer. Mienshao can lure in mons like Gengar with threats of HJK and Turn out to get in a check like Alakazam, thus gaining momentum as Gengar is forced out which allows Zam to set up. Another example would be Weavile, who can force out mons with threats of OHKO and can use the time to set up with SD and proceed to sweep. Simply for this niche, Mienshao should be B+. People say it is beaten by common Scarfers, but these scarfers need a chance to switch in which is not usually available with Mienshao.