Its about how you play the midfield.
Pogba and vidal's offensive contributions are the future of juventus. already they are quite good. With pirlo serving both as the player holding the midfield, and the regista.
Now when taking pirlo away, first, comes organisation. We need a holding midfielder. Both pogba and vidal are wasted there, because their biggest strenght,is their aggressive pressing game, and their danger close to the forwards and their attacking impulses. Make one a covering midfielder and the enemy has MUCH easyer to build up. Right now, we are a hell to play against, with those two effectively making it hard to build up.
Marchisio, has good passing and distribution, he's fine there. But he isnt a playmaker. neighter are pogba and vidal.
So, without pirlo, we can do a few things.
We could play 352, but have the cm's in the buildup close to each other and have tevez drop off in the center. Not ideal but it works
We could play 4312 or 4321, but then we'd have to put marchisio as a cam, leaving pogba to hold the midfield. Wich takes away his offensive value, wich is not ideal
Here is the deal. We need a PLAYMAKER to cover for pirlo and we dont have it. Conte uses Marchisio is a playmaker, but he isnt cut for it and diamanti would do that better