A 22 year old Marchisio was playing for Empoli, and Juve's midfielders were C. Zanetti, Sissoko, Nocerino, Tiago, and Ekdal.
22-yo-Bentancur > 22-yo-Marchisio
It's not really a fair comparison of how good a player will be by looking at x player at 22 compared to another at 22.
Players develop at different ages. There have been plenty who exploded in their early 20s and stagnated or regressed. Similarly there are guys who peaked late in their careers.
I'm a huge fan of Bentancur, always have been. But he is a very different player to Marchisio and I think people should curb their expectations that he will become a goalscoring mid like him or Vidal. He has the ability but his game is completely different.
Marchisio was tremendous for us and I think people look back and underrate him given the other mids at that time. If anything people should think he was every bit as important as Pirlo, Pogba and Vidal to us. Look back at the goals in our first season in 2011-12, he scored so many important ones.
If Bentancur gets close to the player that Marchisio was for us I'd be delighted, he certainly has the ability and attitude to do it.