I guess it's also not even the accuracy. It may be that he's just really comfortable using his left to pass it to his CB partner. But the type of balls ETH likes from his CB are those penetrating through the lines ones like Martinez does. I doubt Varane could pull those off with his left.
Was going to reply exactly this to you earlier. Weirdly I recall seeing Varane making a few decent long switches with his left but when he is playing on the right side of centre defence. So out to Shaw/Rashford. I don't rate his ability to bring the ball forward and play incisive passes out from the back but he is far more likely to do this when on the right side of defence. It means Erik not a fan of him on the left hand side generally when we're used to having Martinez, Shaw or even Evans doing it far better.