Oh its such a shame Ruben isnt here to tell you how stupid you are and how Nibali will never win a gt etc.
But in all seriousness, Nibali had rested and prepared for the Vuelta. Rodriguez had just done the Tour and he hadnt even rested much before that.
Look at Menchov. He didnt do half what Nibali did during the season, but was too tired to perform after that Tour at the Vuelta. Samu skipped what looked like a certain grand tour victory and Andrew, well the less said about that the better. So we cant say that Purito would have been on his best form either.
and despite all that he still won the stage to Pena Cabenga, and crushed Nibali on alto de Cotobelo.
Take Rodriguez's fatigue out of the picture and you have far bigger gaps on those stages and smaller gaps on tt and Bola.
Now take those mountains double them then increase their gradients massively, and take out the tt. What you have left is a picture far more rosy for the Catalan and far less so for the Sicilian.