well, to be honest, i find the DRK battle stance to be... decent (popping all the CDs in anticipation of stones being thrown)

here is the "Sephiroth Stance"

remember that he is left handed, he grips masamune mainly with his left hand on the top.
In this stance, he turns so his left side is facing the camera, sword pointing forward, left hand in front, right hand in back, no crisscross
heres our DRK stance

we are the mirror opposite since the game assumes we are right handed
right side facing the enemy, holds the sword so the right hand is in front and left hand in the back.

apparently this is an authenic medieval longsword stance as per google (albeit with an overexaggerated 'longsword')

the "hanging right" stance



to me, it looks as if most of the drk actions can be carried out authentically, just with a regular sized 2 hand longsword.