In his playstyle, its important that the cm can build up the play.
That was about the only lesser points of vidal. He's not bad at it, but if thats what they wanted, then Marchisio was that much better.
Vidal would also be limiting his game, because with 4 midfielders and a false9 in front of him he'll need to compensate for them. He cant go and press cause nobody has his back. And he is the guy that is supposed to back everyone.
But thats not Vidal's game. His game is to be pressing aggressively and winning battles, and have someone watch his back instead