Probably on paper, but have you seen these kids play, they are fast, motivated and willing to give more than they can handle. Compare that Emerson and Vieira, slow, getting a fat paycheck at the end of the month wether they do their job correctly or not and above all playing without even caring if they lose at home against Pistoese (with no disrespect to Pistoese fans).
Denco mentioned it many times that Emerson and Vieira are not compatible with each other, on paper they are the best central midfielders probably but together they don't combine. It is as simple as this, this combination is wrong. On the other hand Silva and Fabregas are playing well together and thus are producing much more than Emerson and Vieria are.