it's Amanda who is right: people don't change. Jeff in particular gains nothing from his experiences. None of Jigsaw's victims are better off for encountering him. The closest he has to a success is Amanda herself, but the whole point of S3 is that she's another failure whom Jigsaw has to put down.
It's true that Saw 3 involves cooperative traps. All of the people involved in Jeff's tests die, but he was supposed to save them (except for Amanda; Jigsaw apparently relied on Jeff killing her). Likewise Amanda's survival depenRAB on her allowing Lynn to live.
However, the same applies to Saw 2. Eric Mathews was supposed to not beat Jigsaw to a pulp. The people in the house were supposed to cooperate, or at least didn't need to fight each other. It's also the film in which he apparently has a success, with Amanda thinking she is a better person. If Jigsaw is a hero, Saw 2 is the movie in which it happens.
At the moment I'm still a bit confused about Eric Mathews. He failed his test. Does he get given more chances, or does Jigsaw consider him sub-human and just a pawn to be used in his tests of other people?