I believe mienshao deserves a bit higher ranking. 105 base speed is awesome (4th fastest pokemon in the tier, and jolteon isnt that used)
Also, 125 base attack coupled with life orb high jump kick is just destructive. (Not even Full defense hippowdon dares to switch into it if hazards are on field) Stone edge helps nailing Gengar, which is probably the best offensive switch in for this thing, and to finish it all, hp ice deals with the things HJK can´t (Gyara, salamence, gliscor, etc etc )
Regenerator makes up for the life orb recoil, however, its stellar point is the fact mienshao can u-turn, gain momentum for the team, and even cure itself (It isn´t hard at all to pressure a switch with such a powerhouse)
It also resists stealth rock and with regenerator chances are you will mostly see mienshao above 80% health (Or dead). (Even the strongest priority moves need a boosting item to take it down at such health, of those, scizor is the one that deals most damage, however it still needs life orb/choice band. Dragonite must have choice band if it wants to kill, and everything else fails to kill Mienshao at such health with priority). Also, Mienshao has its own type of priority, albeit kinda weak, in the form of Fake out.
Lastly, the issue Mienshao´s counters dread of (Ghost types, mostly gengar) is that u-turn Mienshao can easily bring a pursuiter to take them down.
Certainly it has flaws, but B rank seems kinda low. Just my opinion.
Oh, btw, Protect also works against it, but with Regenerator + u-turn, Mienshao has no issue regaining back the lost hp.