We need more variety of MR items

To be fair, with Merc's, Zz'rot, Locket / Banner, Banshee's, and Spirit Visage, you've basically gotten a full build. Heck, you can also fit Abyssal in there, too. We do actually have enough tank items to stack exclusively MR against an all-magic team.

That's not to say more MR options wouldn't be appreciated, but we really don't need an item that's like Force-of-Nature. Spirit Visage and the upgraded Aegis items already fill its role, so with a Deadman's Plate you've got a FoN with armor, health, and CDR that's split across two items.