Button is a decent driver, but I see nothing to indicate he's one of the best; certainly he hasn't shown it in any other season. In his first season he was outclassed by Ralfy - a second string driver if ever there was one - in his second season he was outclassed by Fisichella (who Heikki beat in his first season). In his third season he beat Trulli, not a bad season really, but then you look at what Alonso was able to do with a roughly equal car the season after and it doesn't look so hot.
At BAR he beat an ailing Villeneuve who was way past his prime in 2003, and scored a good number of podiums in 2004. But, here's the thing, shouldn't a top notch driver in a car capable of getting 12 podiums and 2nd place in the constructors have managed to win a race or two? 2005 was a rotten season for BAR, and Jenson probably got what he could from it.
Then came the Honda years, paired with the second-string Rubens he beat him in 2006 and 2007 and then was beaten by him in 2008.
That's not the record of one of F1's greats; it's the record of a decent driver a little off the top tier. This year he's been given the best car on the track and made the most of it - credit to him - but he's not the best driver on the grid by any measure.