One reason that I disagree with Cosby's assessment is that, much of the time, Archie did learn something, even if he didn't admit it. One episode that I remember is where they're visiting Edith's niece, and Archie realizes that the niece's roommate is actually her girlfriend. Archie wants to leave right away -- this is wrong and they're sinners and this is not a house he wants to be in. Edith says no, this is her niece, they're staying. They argue about this, and Archie says, "Don't you think that God's up there judging right now?" And Edith responds, "Well of course he is. But he's God. You ain't." And Archie, with some grumbling, agrees to stay.
And that sort of thing happens in a bunch of episodes. Someone points out that Archie's wrong, and although he won't actually say, "I was wrong," he does the right thing, or somehow fixes whatever his previous statements had screwed up.