There’s a difference between people who had a chance to become champion, but didn’t take it, such as:
Stirling Moss (1955-1961)
Juan Pablo Montoya (2003)
Ralf Schumacher (2001,2003)
Felipe Massa (2007,2008)
Rubens Barrichello (2003,2004,2009)
Others simply never had the chance to be champion, such as Jean Alesi.
As it’s been pointed out, 2003 was his best chance, when the Williams was finally equal or faster than the Ferrari. But Ralf didn’t come close, and Juan did better, but couldn’t get past Barrichello without spinning him off.
Williams was definately the best car in 2003, otherwise Schumacher and Raikkonen would’ve beat Montoya comfortably. Ralf was a championship contender after france, but only scored 5 points in the last 6 GP’s (LOL).