100m for 28 years old CM, who is not always showing up in the big games is a good price.
On the other hand he probably still has 4 years in him at top level, is integrated with the team and could be hitting his peak just now.
Looking at the stats:
17/18 44 7G 14A
16/17 47 8G 14A
15/16 (Roma) 41 12G 13A
Considering his position now in Juve his stats are just insane, much better than Pirlo in his best years here.
Stat padder or not this numbers cannot be ignored when we are speaking about him leaving Juve.