Suuureee. Pirlo simply was the reason we got the 4th place that qualified us to the CL that we won with him being super important, and then the scudetto were he was again if not the best top 3 of the best of Milan, also was the guy that took away Totti's star role in the NT (mayor words) and if not best was top 3 of the reasons why Italy won the WC. Needless to say Pirlo first had a completely different role in the field, and to a point one can say he is the one that started the new wave of DM-CMs.
Sure, Xavi alll that time, even with the stability of being in the same club since he was made, was already better than Pirlo ever was for Milan. Short memory or lots of biased, think it's the latter.
No one is denying that Xavi right now is the better, but you're missing the point (probably not missing but wanting to miss the point) that is being made: Xavi, as well as Pirlo, as well Fabregas, as well as any other CM you want to think of needs certain type of players surrouding him to make him be effective.
Xavi is lucky atm of being in a team that has perfect off the ball movement, and that has lots of pace, and on top of that he is also playing in a league that provides him with the space needed to perhaps look even better.
Now do you really believe if we just swap Xavi or Fabregas or anyone you like with Pirlo and leave everything else at it is we would be a better team?