Hello Rizzoxiii!
We wanted to give both Deft Maneuvers and Powerful Maneuvers a movement impeding option. The actual implementation is a bit of a mix of Stand Still and Scorpion Style, and the name is really more of a metaphorical adoption of hamstring (impeding movement or limiting activity) rather than a literal attack on someone’s tendons.
Also, Deft Maneuvers also improves a character’s ability to feint, so the disparity between Deft/Powerful is not quite that large.