I don't know how you are totally missing the utter lack of even remotely comperable balance here for the sake of nit picking some CD times but let me break it down further.
WAR Bloodwhetting - 25s CD. 400 potency heal per target hit by any attack. Lets just say there are 5 targets in a small AOE pull not wall to wall. That is a 2000 potency heal per AOE cast for 8 sec. Say you somehow only managed to get off two AOE attacks, which is really, REALLY bad since they have a 2.5s gcd on average and you also have ogcd like Orogeny that can be woven in between casts which will also proc the heal, but just to keep things conservative and simple. That would still be 4000 potency healing every 25s. That is easilly more than a full healthbar of healing (more counting crits). On top of that you get 10% damage reduction (20% for the first 4sec), AND a 400 potency barrier.
DRK The Blackest Night - TBN costs 3000 MP. Even with a 15s CD, you have to actively plan your DPS to balance keeping up Darkside with having at least one charge of TBN available for when it comes up. WAR doesn't need to think about anything.
The ONLY thing TBN does is give you a 25% health barrier. No damage reduction. No healing. NOTHING. IF it breaks (and on 5 targets it frequently won't no matter how much you "calculate"), you get a free cast of your 3000 MP damage skill. Otherwise you are out the MP for a wimpy little 25% shield with no mitigation and no healing.
WAR - Heals full health multiple times, gets active damage reduction, AND a barrier, with NO planning and no resource management. Doesn't rely on timing healer stuns through chat communicating with randos with our 2nd set of hands. Actively contributes to DPS WHILE healing increasing the efficiency of the entire run.
DRK - Gets a wimpy 25% health shield and NOTHING else AND it costs MP. Healers hate you.
Yeah. This is fine. Totally wonderful game design and balance. Let's keep defending it.
I mean objectively that is like comparing apples and orangutangs! The two signature job abilities are not even remotely in the same league! This is OK?
Honestly this game has over a dozen DPS jobs, but only one serious tank (WAR), one mid tank (PLD) and a couple lower DPS jobs that can use tank role mitigation and have some gimicky job mechanics that are inferior to WAR in every way.