Pirlo is indead the best regista in the world, but at current age, the issue are the downsides of wel, aging. loss of pace, agility and stamina.
You can argue he doesnt need those, but when he turns away from a defender, pace and agility make it that much more effective.
De rossi isnt a regista, but plays in the same area of the field. However, getting de rossi means we'd be needing a new winger, that is offensively extremely good, cause has to compensate for lack of pirlo's creativity
can we get that winger ? not sure