Ferrari's update was largely aerodynamic, but its appears that Mercedes biggest advantage was mechanical. It been pointed out that the first two sectors, which has the more high speed corners, reliant on aero performance, Merc were faster than Ferrari by a few tenths, but the Merc absolutely monstered the final sector in which is much lower speed. If that carries on, then you'd expect to see a rout by Merc at Monaco and other tracks that have twisty sections.