http://forum.square-enix.com/ffxiv/t...801-08-2015%29
Discusses directional based attacks of MNK and DRG and how NIN do not have such limitations but instead a "complex element of using mudras".

By making the mudra mess-ups trivial, you would only expect NIN to be nerf'd in other areas to balance this.

They are looking into mudra lag - but it is nothing they can do on a short time without completely overhauling the system.

I don't think it's proper to be comparing Stoneskin II to this as it is nothing more than a QoL spell, which they made the restriction to outside of combat only as it can be overpowered during combat.
What you want is pretty much ignoring the complex use of mudras that the developers have in mind.