One hand over, one hand under solves the mystery.
Having both hands semi supinated using an EZ Bar is safer & the idea is to hit more of the Lower Lats evenly which you cannot do with a mixed grip, also one bicep is under more stress with a mixed grip which could result in a tear.
A semi supinated position also involed more Forearm flexors & Brachialis which lessen the risk of a tear.
However i believe Dorian changed later to a standard grip on his rows due to injury.
I have in the past used a mixed grip on chins but i wouldnīt do it nowadays.
