Don't get me wrong, I love my barbell workouts also. It just seems that all Cathe's leg workouts of the previous two decades were similar in their use of the barbell for standing leg work, with dumbbells for lunges, etc. I did these workouts assiduously, but they did not stop me from getting running injuries.
What's great about the newer leg workouts is that they are equally punishing (!), but with way less weight loads, so we are actually working different areas of the muscles, so if you combine the two types, say GS legs with Xtrain legs, you get the complete package! We are better protected against injury from this new emphasis on the large and the small muscles of the core and lower body. And it should also translate into greater endurance, greater power.....
Clare