They already nerfed it multiple times.
So your logic here is just a fail.
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6 seconds of no damage is do-able on some fights, it's going to be less useful on say mythic than N/H.
I doubt many tanks are going to go zandalari just for it, it's not that great.
The whole interrupt on dmg taken isn't super realistic. For four seconds it was potentially op in some situations, now a 100% self heal over the course of 6 seconds requiring no damage is at the level a racial should be.