BiS Shield

[YuriRamona]

HA blocks for 31-32%, Noct blocks for 42% (referenced from above)
Beak hits for 7638
HA block would hit for 5270
Noct Block would hit for 4430

Neither will make any difference for your mages and that's the hardest hitting single attack in the game.

It's not the Ravensbeak that kills you. It's the auto-attack/cleave afterwards (with possible crits) that drops you. Having 800 additional HP could definitely be the difference between life and death. Not to mention if healers derp and fail to top you before Ascent and Dive, both of which can take half of your health.

2000 damage per claw.
Noct 80%
4 of the 5 will be 6640 damage.

HA 90%
4 of the 5 will be 7520
5 of the 5 will be 6624

Neither scenario will kill a t9 PLD.
And again you would never be in a position of only using Bulwark.

I'm not sure where you're pulling the 2000 figure from, but it's certainly a greater range above 2 stacks. Bigger blocks (though rare) can mean that you could live.