Rupture Tendons needs a nerf IMO, it's way too powerful, and this isn't just Mordus. There are tons of wonky enemy AIs that will just run to their deaths via RT.
I don't know.
I've read plenty of stories about how overpowered it is combined with polymorph... But I didn't use that combo, and in plenty of other scenarios (almost all of them, in fact) I noticed that if I use Rupture Tendons on an enemy, that guy typically refuses to move or moves just by teleportation.
So I have no problem whatsoever with that skill. I surely won't complain for that ONE OR TWO times it actually works on someone.