How important is defense for a PLD...?

[Kryzen]

It only works in OP's example because his HP is high enough without it for that single instance. It's the same thing as that group that did Titan HM in swimsuits. This only works with PLD as they have many cooldowns to mitigate damage and their tanking stance is default 50% damage taken. So as long as you have enough HP to survive a big hit or two, then you can do it in your undies. This is impossible for Coil, however.

Pretty much sums it up