Look at the manga and the anime, and you can test this for yourself actually since it is an actual technique in bujinkan. The sword is supposed to be unsheathed at the instant the left foot comes down and doesn't move throughout the stroke until it's completed. In shishio's case, he has to pivot and do it again but its the same. When you draw with the right foot in front, the swing only uses your arm's strength, the left incorporates the legs and chest to a greater degree along with the hip rotation. That's why kenshin could not defeat hiko's kuzo ryu sen because of his shortcomings in strength and pure mass, the ogi made up for that.