Board Thread:User Wiki Issue Reports/@comment-24324533-20131222092414/@comment-24057727-20131222093357

Vesture of Frost only gets a single element bonus from guild, while Witch's Robes gets a double element bonus. It's for that reason that most people don't use single element legendaries.

On the other hand, single element epics have a higher base stat to offset the lack of a bonus, and they also have a lack of an additional elemental weakness (you'll understand if you've fought Red Kal+ recently) - so single element epics like Northeners can brute force their way through most teams (unless you have an elemental weakness).