really, maybe i had no good experience with mnk tanks, but i don't get all this excitement about it
wow, you can go mnk + whm and duo wathever you want, the mnk keep blindly hitting and the whm spams cure, at the end of the fight you see no drops and go home happy!
as a nin, i nealy never need a whm to cure me. i usually duo with a blm, we proc yellow and red 90% of the times, with stun and violent flourish i hardly take any dmg, hate reset is not an issue, just throw a hyoton san.
i'm not underestimating mnks, but for low man situation in aby, i'd rather go with a multi purpose tank and a multi purpose healer, than with a big punching ball followed by an ambulance.

the problem is always the same, /nin? no provoke waltzes and so on
/war or /dnc? no shadows
u want both? NIN/DNC and DNC/NIN are the way to go

that said, i'm sure in particular situations MNK is unbeatable, but in abyssea nin and blm can duo nearly everything, and they get better drops