One of the problems with arguing about who is the greatest driver is the fact that in racing the driver is one of two primary variables that determine whether there is a win or not. The car's performance obviously has just as much to do with it.
To remedy this dilemna, I'll propose a new system. The drivers should not be assigned to one team. The drivers should rotate from team to team, taking turns driving for each team. Let's see Massa take a shot at it in a Spyker. I wonder how Sutil would do in the Ferrari? Under this system you could more accurately determine who is the best driver and who builds the best cars.
No one needs to tell me about the complications this would cause, it's impracticalability (is that a word?), or the various shortfalls of the plan. It would be interesting.