People think Conte made our defenders look good. But Allegri has taken it a level higher. When you press high up the pitch and hold possession when you win the ball, your CBs have very little pressure.
This is why people think players like Pique are "world class". Allegri has taken away all the danger for players like Bonucci. He no longer has the ball and he no longer has to defend in his box as much. Actually, most of his best tackles are now in the other team's half (although I have to give him credit for his match against Fiorentina, it was excellent).
Chiellini still sees the ball in a 4 man line, because well, our opposition lets him have it. Besides Buffon, Chiellini is always the most open man for us because he presents the least amount of danger.