Not really anything to do with balance, but some ideas to make the tank cooldowns more flavorful and interesting.

PLD - Hallowed Ground - After hallowed ground ends, gain "Blessed" for 10 seconds, reducing damage taken by 100%. This reduction decreases by 10% each second.

WAR - Holmgang - If you are reduced to 1 hp during Holmgang, gain "Bloodied". When Holmgang ends, if you have Bloodied, you immediately gain Infuriated/Uncontrollable and reduce the CD on Infuriate by 30s.

DRK - Living Dead - Your attacks leech 50% additional health during living dead (souleater leeches 150%). This increases to 100% additional health during Walking Dead (souleater leeches 200%). If you are alive at the end of Walking Dead, you immediately gain the effects of Sole Survivor (aka recover 20% hp and 20% mp).

PLD is focused on having additional reduction, I imagine WAR to be more offensive and angry, and DRK being leech vampire focused.