Bonucci is a good defender. He's just been unlucky with Juve.
Don't forget, he was also Italy's best defender under Euro 2012.
Italy's defense was only really challenged vs Spain and we have all seen how good of a defender Bonucci was there and then...
Bonucci is a horrible defender, he cant even achieve a sliding tackle, he also lacks tactical awareness, he is quite a reability and this was proved time and time game.
He was very lucky this year though, because he had 2 great CBs around him to make up for his messes and most importantly, our possession football and great performance, eased up the pressure from our defense.
When Bonucci was exposed without midfield cover and great partners, he was pretty horrible, at least for 3/4 of the season and the whole season last year...
Masi at his age will be a better tackler, with better tactical awareness and positioning and much less clueless with the ball on his feet.