Definitely not great numbers by any means but factor in the fact that he is barely allowed to take chances and the play it safe mentality that a QB just has to manage the game has been drilled into his head since he was drafted and you can't expect much more.
And the reason that he lost his job is because Singletary was trying to save his own ass by scapegoating Alex Smith as the problem with the offense, just like he did earlier with Jimmy Raye and like he is now doing with Troy Smith. But, even with all of the changes, the offense looks basically the same as it has all year (maybe even worse). You know what the constant was during all of it? Singletary handcuffing the OC and QB.