Marchisio shouldn't play as a b2b mid anymore, simply doesn't offer enough offensive output to be valid solution for this role. It is more evident against better teams with strong midfield area. He has these long periods when he's completely out of the game, while this role requires more consistency and better productivity. We have better players to field there and Marchisio can contribute much more as a CDM; IMHO he's better at this point than Pirlo, at least both b2b mids be it Vidal, Pereyra or Pogba can play up front in more relaxed manner, knowing they have good defensive player to cover for them and mistakes they'll certainly make during the game.