I wanted to provide information for all players to understand PvP damage / prevention.
First off I need to make sure everyone knows that Damage reduction / prevention is not additive, it is multiplicative (you multiply separate damage reduction sources instead of adding them together). This means you do not add together all your damage reduction sources to obtain your damage prevention.
Damage Reduction Example:
–Defiant - 25% (not accounting for missing HP)
–Armor - will assume 2X obsidian / 1700x2
----Armor gear - warrior 250x4 (chest, helmet, ring and amulet give 250 AR each at level 100). Rogue provides 150x4 for AR and Wizard 75x4 AR.
–Resist - will assume 1x obsidian/170
----Resist gear - 100 (Chest 10 + Helmet 10 + Ring 10 + Amulet 10 + Pet 10 + Trophy 50)
–Synergy sets (Example to give understanding);
----> Armor - Plagued 25%/rank (75% with one set) / Battle Mage 20%/rank (60% one set)
---->Resist - Cerebral Vortex is 12.5%/rank or at Rank 3 is 37.5%
Important note: you gain additional synergy above with HP (Plagued 1.75 + Battle Mage 1.60) and MP (Cerebral Vortex 1.375) that is in addition to the damage reduction.
Defiant 1-0.25 = 0.75
Armor 1-(4400x1.75x1.6)/((4400x1.75x1.6)+(20x1000)) = 1-0.3812 = 0.6188
4400= 1700+1700+1000 (warrior gear)
1.75= Plagued at Rank 3 [1+25%x3 or 1.75]
1.60= Battle Mage at Rank 3 [1+20%x3 or 1.6]
Resist 1-(270x1.375)/((270x1.375)+(20x100)) = 1-0.1566 = 0.8434
270= 170 + 100 (gear)
1.375 = Cerebral Vortex at rank 3 [1+12.5%x3 or 1.375]
Overall reduction (If you are not facing eternal bloodless trophy with 20% AR pierce) - not much effect though… If you are facing Eternal Bloodless Trophy with 20% AR Pierce then you Armor damage reduction would become;
4400x0.80 or 3520 Due to 20% AR Pierce
(3520x1.75x1.6)/((3520x1.75x1.6)+(20x1000)) = 1-0.33 = 0.67 (only 6% difference from above).
1-(0.75x0.6188x0.8434) = ~ 61% Reduced Damage
There are effects that will make your damage reduction not what is calculated above. If you are not using 3x Perseverance then you will take Bleed Damage on top of your damage reduction. I am not recommending using 3x Perseverance but 2x is typically a good investment. Any critical strike or deadly strike will make your damage reduction much lower. Using Eternal Flawless Trophy will lower the ability of players to Critically Strike you since the critical strike cap is 24%. Exposed and Ruptured mythic also reduce your damage reduction.
If you have any further clarification or understanding questions please feel free to ask. This information should help you to make better decisions about how to decide between damage reduction investments.