So, Casper is super duper correct. Like, super duper.

For one, let's just say the op's estimate of like 1-2% damage reduction from full parry was right. Yes, this sounds trivial, but you know what else only reduces about 2% damage over time? Hallowed Ground.

Rampart: 20 seconds every 90, 20% reduction = 4.44% DR over time.
Sentinel: 10 seconds every 180, 40% reduction = 2.2% DR over time.
Hallowed Ground: 10 seconds every 420, 100% reduction = 2.38% DR over time.
Convalescence: 20 seconds every 120, 30% healing received = 5% HR over time.
Total increases from cool downs:
9.04% DR over time
11.58% eHP over time
16.58% HR over time