Maybe RNF will somehow reduce Magic Damage for ... everyone!
Monster use's Large Area Magical Attack
Everyone: YAY RNF Saved US!!
Monster: Hmmm
Monster use's Large Area Physical Attack
Everyone: Ohh noes!!!
MDT is the easiest to cap. Shellra V alone is 27.34%, 29.29% if they have the augmented relic armor. Only need 22.66 / 20.71 in DT/MDT to finish capping it out. You can get 10% DT "free" without touching your major gear slots via Twilight Torque / Mollusca Mantle. Get a nice Dark ring or two and you've easily capped out MDT while being at capped gear haste.
PDT is a different story, without an Apoc your not capping PDT and haste, especially with being nerfed.
We need a "Magic Tank" about as much as we need another pet class.