I don't really agree with that. He wasn't even a character, really. Because he had no motivation or even personality. He wasn't even himself, because for the majority of the movie, he was basically a cute pet with no memory. Then at the end, he got his memory back and returned to being the character we saw in the first 5 minutes of the movie. But during the middle 100 minutes, he was nothing. The two Decepticons were characters maybe, for the little screentime they had.