/d'oh (Noticed Earth Staff only reduces Physical damage)
Nvm, then.
EDIT: I feel I should clarify what confused me is that I looked up the Blue Magic spell 1000 Needles, and it said that it was a Magical Blue Magic spell, aligned to the element Light.
But, I had forgotten that sometimes Blue Mages get different versions of their spells than that monsters' actual abilities.
That led me to think that this was tested in PvP against a Blue Mage's 1000 Needles, rather than a Cactuar's, as it actually were.
Ah, well. As stated below, though, a main job Paladin could use Rampart.