Just saw the Castrol rankings and it is indeed flawed, in the sense that it does not measure the 'capabilities' of a driver but his accomplished feats.
The very best driver in the world would NOT score well in this setup simply because it is a measure of the car/team/skill/luck, POS car/team, only by luck any success.
Look at how F. messed up Kimi, or BMW and Kubica a couple of times in Qualifying last year as an example.
No way is Nico Rosberg, Jarno Trulli, Mark Webber, Rubens B. or even probably Kimi, better than Alonso, NO WAY!
Lewis H. may be, but just, and then maybe not in a true even-even test, (Lewis was favored some amount by McL/Dennis, but hard to quantify). (Alonso was just to mention a single driver who is better than he is listed)
This is one reason why there really should be a series where we could actually see a 'Race of champions' so to speak, a true cross 'race' cultural (F1-Indy-Rally-Nascar-DTM-....) set of races with measured equal cars.
It likely would have to be in several car types, because any single car type would likely favor the current skills of 1 driver over another, maybe karts or some different car type. Hey, how about racing Diesel trucks!

(Joke, no thanks!)
But the Castrol list is flawed and only partly legitimate effort but we all know some drivers really are better than others and the list is incorrect on this order. (Where's F. Massa in the top 20??)
Nice try Castrol but keep honing that algorithm!!!!