I’ll guess pre power steering required more leverage. Have always used 7/5 position, and encouraged that to my kids when teaching them to drive. Arms are more relaxed, can react quicker in either direction and have greater range of motion. Over correction when highway driving seems less of a problem as well. See others who want a death grip on the wheel…usually in the 11/5 position.
7/5 and relaxed position is common to many sports that require quick hand reaction, why should driving be any different.