Feels to me like you have misunderstood the message. MFA is available for (very) small amount of front/back focussing due to manufacturing tolerances between the distance from rear element to the imaging sensor plane and AF module (in an ideal world both distance should be the same but even knocking body slightly can misalign them ever so slightly).
MFA is never for optical issues or front/back focussing caused due to optical misalignment which is what your email also seems to suggest.
This is why Samyang providing MFA through a dock doesn't make sense. to some extent I think its in there because Sigma/tamron provided that feature in their docks which were for DSLR lenses and samyang just wanted to join the Kool kidz camp.
Also MFA isn't complicated its actually rather simplistic in what it does. If you do in camera you are telling the camera that the distance it thinks it's achieved focus at is that distance +/- MFA value (and it'll signal the lens accordingly but the lens doesn't know any better). If you do it in lens, the lens will move the focussing element by +/- MFA value you set in lens (and body doesn't know any better). do in both and you are overcompensating