RB every time this season, of course.
Well exactly, and quite possibly for the previous three seasons too. Of course, that's not to say he wouldn't have come out on top if we could follow the balancing hypothesis and put every driver in a RB, but how can we even guess, let alone know? I'm sure, though, when several outstanding drivers are in competition, the car really does make a difference. The number of points scored by fairly average no. 2 pilots such as Frentzen, Barrichello, Irvine, Coulthard etc. illustrates the point. Massa came within a corner of the title, but you'll have a job to convince me he's ever been anything like the best driver in a race, let alone over a season. Was Button the best driver during the season he won the championship, or simply a good one in the best car? To my mind, the best drivers are those who get something out of their cars they've no right to. I think Alonso has done that this year, as has Ricciardo and possibly the Lotus boys (definitely at Suzuka). Arguably Hulkenberg too, although the parallel if less spectacular improvement by his team mate could indicate an engineering advance.
Vettel is, of course, at a disadvantage in this argument, having the best car the best car to start with, but although he's undoubtedly the best tactician, and has the single-minded ruthlessness of all champions, I'm doubtful whether, purely as a driver, he's 4-in-a-row better than everyone else on the grid.