New Formulas Simplified

It may seem odd, but is it possible that this new PDRate just tells you how much of your damage it will affect. For instance, on Zakum with 25%, it will normally only take a MAX of 25% damage off (1000 normal, 750 after), not counting level differences. Also, maybe def up now affects this PDRate, too.

PDRate is just simply how much percentage of damage is taken off. You'd be doing 75% of your expected damage by your damage range at zakum, for example, before defense. This works the same way that monsters' defense up buffs work now, reducing your damage by a percentage. Most defense up buffs from monsters have x=85 which means -15% damage.