Messi won it in 2010 because he was the best player in the world, not because he was the greatest talent.
For the past 5-6 years no player has reached the level of performance of Messi and Ronaldo. When people bring in players like Sneider, Robben, Ribery and whomever else in the comparison, the mistake many people make is that they compare Messi and Ronaldo to themselves first and then they compare them to other players. So for example, the 2009 -2010 season wasn't Ronaldo's best, people rightfully pointed that out, but then made the mistake of using that to say that Sneider performed better(Sneider probably had his best ever season then). The problem with this kind of comparison is that you're holding Ronaldo to a much higher standard than Sneider, and then using that against Ronaldo. To illustrate: you're comparing Ronaldo's level of performance against his usual level of performance(The higher standard), and then comparing Sneider to his usual level of performance (The lower standard), and because Sneider scores better on his standard you make the mistake of saying he had a better season than Ronaldo, when in reality Ronaldo's worst season in 6 years was individually better than Sneider's best season ever.
Fact of the matter is that the Ballon D'Or is an individual award, that recognizes the best players in the world, it is in effect a measure of individual performance. You could say that Ronaldo didn't win anything in 2010 while Sneider won everything that year, but that's immaterial if Ronaldo's individual performances were a lot better but he was let down by his team. The fact is, Ronaldo and Messi have been a level above the rest for the past 5-6 years, and they rightfully have always been #1 and #2 in the rankings.
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So if someone is world class all season long, and is levels above all other players for 40+ matches, you wouldn't consider him the best player in the world if he was neutralized in 2-3 games? That doesn't seem fair, I would think consistency throughout they year would be more important.