They're spells, not special attacks, so they can't be pacified. You'd be surprised at how few actual "special attacks" bosses have and how little Pacification actually ends up doing.
It depends upon how you define "meaningful". If you define it as "actually putting pressure on the healer", then, no, nothing that the first boss in AK does is actually meaningful. If you define it as "forcing the healer to use a GCD to heal instead of DPS", then, yes, it is meaningful. Iron Justice on the Dullahan trash isn't really "meaningful" damage in the first sense since any tank will be able to survive it easily and any healer should be able to heal through it no problem, but you're still going to tell tanks to stop eating it.It's not like the boss can actually do enough meaningful damage to matter.
The point I make is that there are a *lot* of tanks out there, especially PLDs because they're used to avoiding damage with Shield Bash and ignoring any other avenues of ability avoidance, that will take damage that is easily avoidable. Bad tanks just eat it and expect their healers to pick up the slack. Good tanks just avoid it outright because damage not taken is better than damage healed, even if the end result from the tank's perspective is exactly the same.
Who says I don't do that? I get on the case of anyone that takes avoidable damage. I yell at BRDs that don't interrupt the third Tumult to reduce the massive raid damage on p5 Titan. I yell at DPS that just stand there instead of running from the blob boss in WP or eat the inhale on the first boss. I yell at DPS that eat Catastrophe, Murder Hole, or Thunderstorm in AK.Why don't you go yell at the healers that insist on standing in the giant red radius of death (not behind a pillar) because they don't know how to dodge?
I get on the case of anyone that just takes unavoidable damage often enough that it's apparent that it wasn't just an isolated incident. However, that's not what this thread is about. This thread is about what tanks, specifically PLDs, should not be doing and eating easily avoidable casts is one of those things. A bad PLD is going to just eat every single one of those casts; a mediocre PLD will stun or silence them; a good PLD will recognize that stunning or silencing them is a waste of resources and just dodge them at the cost of nothing.