He's a natural leftback that actually performs good as center back.
Nah, i wouldn't say that LB is his natural position. His body contruction, his ball control (pretty bad), his strenght, heading abbilities, marking, positioning, crossing (not good enough) scream Central Back. You look at his "nature" and you see a CB there. So his natural position is actually CB.
He started as a LB but that doesn't make LB his natural position. It only means that some coach early in Giorgio's career wrongly saw a LB in him. Or maybe the circumstances required from him to play LB back then.
One of his coaches ( i believe Casiraghi at the u-21) rightly noticed that Chiellini makes a better CB than a LB. Since then all his coaches consider him a CB, and rightly so.
Giorgio is simply too rough and too brutal on the ball. Very clumsy with the ball at his feet. You simply can't ask from him to play passing game, to make sweet crosses, to dribble opponents. I seriously don't see a LB when i look at him.