well that blockstring was just one of many examples, I'm not saying you should 5C everytime after a ragna 3C or to think that every ragna uses that blockstring. And the reason I say 5C>2D is because for that situation after being pushed back a bit by ragna's attacks, a 5C>6C either won't reach or the follow up air combo won't. Of course if you are well within range then go for whatever combo you deem best. My point is although ragna's 5D may seem unstoppable, a well timed attack during it's startup can give you a CH.