To answer the question you asked: you'd get 120 def for 100% of 20 sec with the PVP relic. Assuming perfect activation with the def proc relic, you'd get 32 def for 70% of 20 sec as well as 582 def for 30% of 20 sec. That's an average of 197 def/sec.
Wouldn't it be 32 def for 100% of 20 since its a static buff? After that it makes sense. And I hear ya about it not being perfect. Bottom line for me is that it seems to give better 'overall' mitigation than the PVP one even with some pretty bad RNG.