so in the long run, WAR really only gets somewhere between 10-15% persistent mitigation. PLD always gets its 20%
Just a reminder, heal buff % cannot be simply compared to damage reduction.
100 -20% = 80

10 hits => 800dmg on PLD, 1000dmg on war
+15% on a 800hp heal = 920hp

To have those 1k hp healed back you need a permanent 25% heal buff.