Ah, but that's not 1:1 movement. Those are gestures, as seen in the video above.
The sheathing movement can be understood as a gesture and probably even changed in the animation based on the speed of the motion, but again that's not 1:1.
What if I do the motion very slowly? Will the sword on the screen follow my hand every step of the way? If it has no data for a mere moment. If I move it too slowly for it to detect (any movement other than tilting, that is) how will it know where my hand is? It's not like "ping pong ball suit" motion capture, where the position of the ball can be tracked from multiple angles on a second by second basis. An accelerometer tracks a jerk, a swipe, a thrust, a direction, a speed. Not a position in 3D space.