His influence in the defensive phase is hardly debatable. The numbers are hard to argue. Conceding 7 goals in the opening 15 rounds is the 4th best result in the 21st century, not for Juve, but in serie A overall. The best is Roma's 5 conceded goals in 2013/14, then Allegri's Juve in 15/16 and Capello's Roma in 2003/04 with 6, and then this year's Juve defense with 7.
Yes, various factors contributed to this result. Serie A's attacks are obviously weak, and this same Juve conceded plenty in the CL. Teams did miss a penalty and chances against us in the league. We are a defensive team, we are yet to play Napoli, the team with the best attack, and so on and so on. But you can't come up with the 4th best defensive result in the league in 22 years or so by sheer luck and by coincidence.