You could block the first hit of GH and try to punish, but he could use the followup and get a CH. I'd rather burn 623D than wait there to take that risk. Heck you may even block the first hit and do nothing because you thought he would followup, and then he could jsut restart pressure again.
Like I said in the combo thread, the j.D > falling j.C > Dash 5C > 2CC does not work against Ragna in the corner. The 2C may blue beat and the 2CC will indefinately whiff.
Also, lol PK.