It's not as rear as you think: Alaba, Marcelo, are other examples. So is Milner. There are more, but that's neither here nor there. The point being missed here is that there are multiple ways to win. Guardiola has chosen the way he wants to win. I'm simply saying certain players are more valuable to such a style than others.
But your retort, like that of most will be clouded by the 'Bravo can stop shots' fallacy. It's not an either or proposition. There are players who can defend who also have the ball skills. Matter of fact their ball skills reduces also the amount of time they have to defend. Depresses the constantly out of possesion opposition and improves the skilled defenders success rate when they are in fact defending.