Would Cadel Evans have won the '11 Tour if Andy had ridden tactically better, or if Alberto had skipped the Giro?
Would Wiggins have won the '12 Tour if Froome had been allowed to ride for himself?
Would Froome have won the '13 Tour if Contador had arrived in '11 Giro form?
Would Nibali have won the '14 Tour if...
It can go on and on. In some cases there might be a "probably" answer, but probably not a conclusive one.
And Nibali - though about to win - is in a no win situation here. If he returns to the Tour and defends his title next year, then the claim from some will be that Froome was never able to return to his past form and that Contador is now past it (he will be 32). That may well be true and it may well be that Nibali's best can never come close to that of his rivals, but it is very difficult to make a strong argument either way when there are so many if's and but's.
Would Wiggins have won the '12 Tour if Froome had been allowed to ride for himself?
Would Froome have won the '13 Tour if Contador had arrived in '11 Giro form?
Would Nibali have won the '14 Tour if...
It can go on and on. In some cases there might be a "probably" answer, but probably not a conclusive one.
And Nibali - though about to win - is in a no win situation here. If he returns to the Tour and defends his title next year, then the claim from some will be that Froome was never able to return to his past form and that Contador is now past it (he will be 32). That may well be true and it may well be that Nibali's best can never come close to that of his rivals, but it is very difficult to make a strong argument either way when there are so many if's and but's.