His greatest asset is his intelligence, something rare nowadays. That's why stats don't tell the whole story, specially related to this guy. And he clearly is a very confident person, he seems to have the needed personality to play and shine at a giant club. Stats also don't tell this.
The price is very steep, but if Juventus want to sign the guy now it is what it is. We are overpaying to secure it now. We could maybe hardball Zamparini and wait till the end of the mercato to sign him for 20M. But this would be a low chance possibility, since in all likelihood PSG would come calling with a stupid offer. And Inter was really pushing for him as well (maybe only to inflate the price). Even Roma could be a contender later in the market, after they sell Pjanic and Nainggolan.
So I understand why Marotta did this, and in view of the fact that he's a player with rare characteristics (intelligence, great passing, vision, personality) willing to play for us, I think he's doing the right thing. Creative players are such a rare breed nowadays in football. With Pogba and Tevez on the verge of leaving, this team will need creativity to come from other players. Dybala is one of them.
I don't know if he will explode, but chances of a complete flop are low, because intelligence, vision and confidence are very solid features. Even if he becomes only a rotation player, we can definitely get 20M + back later on a sell.
And his salaries are realitively low.