There's no two ways about it- on raw pace Button is behind Hamilton, Alonso, Vettel.
However, he is an absolute craftsman in races, and in the one chance he had in a dominant car, grasped it with both hands. Ask yourself- would Vettel, Alonso, or Hamilton have won any more world titles than he in those same cars? I very much doubt it. Would they have had more poles? Yes. More race wins? Probably one or two more in his McLaren years but not many given that they were up against a genius 4 years of Adrian Neweys Red Bull and would have had top class racers as a team mate.
He's mixed it with people who are going to go into the all time great categories and come out with a World Title, 15 race wins, the greatest ever race win in F1 history in Canada, and the respect of every team mate he's gone up against.
He doesn't design the **** heaps that he has had to put up with every year in his carer bar 2009-2012. 15 race wins in 4 seasons in competitive cars is very good (not great, but very good given the competition).
I hope he manages to get back on the top step or the podium one day- he owes no one anything and has been a brilliant character in F1 for all these years. Coulthard could not lace this guys boots as a driver.
Big respect to Jenson.