Sanchez may be physically larger, but that doesn’t make him more physical. He’s often getting knocked off the ball and off his feet. I think he’s not got enough lower body strength and hasn’t learned how to make up for that lack (lower your centre of gravity). If you watch him he’s all about shoulder charging, no bending his knees to push/protect the ball with his hip and thigh strength.
Also, Sanchez can’t play on the left, or centre CB, he is just Romero’s backup, no more or less than that. We need a LCB in the summer.