With two exceptional cars you can afford one mediocre driver. With two mediocre cars you need two exceptional drivers to compete in the constructors championship.
Ferrari now have two great drivers. Massa is nice but he is simply not fast enough unless he is in an exceptional car. I'm not saying he is slow but I doubt Alonso, Hamilton, Vettel and Kimi fears Massa one bit but they do fear each other.
That said I really hoped for Kimi to stay with Lotus. I would have absolutely loved for Lotus to win the championship and show that talent ( driver and constructor ) counts for more than the deepest pockets.