Yeah the nova, kit fox, and ebon jaguar all have no torso twist, but that is not really an inhibiting factor to their fighting due to the simple fact that the design is meant to have very versatile legs that can pan over quickly, so it turns with a relative speed to that of a torso twist, especially the kit fox.
There is also another design element at work here. The fixed leg mechs are fixed not just for appearance, but because they make a more stable firing platform for heavier weapons, as they can lock in place. That is how the Kit fox is able to hold such powerful weapons that are nearly impossible to fire while moving, like the Gauss rifle (Yes, in cbt unless you really like missing, you got to stop to fire the big guns). The fixed legs are more stable so that the legs take the shock, so that the mech does not rock like normal mechs after firing, which makes the Ebon Jaguar a very deadly heavy weapons mech indeed.