This is true. The Joker and the Goblin may be in the same general category, but they're not at all the same. For instance, the Joker's obsession with Batman is of a totally different character than the Goblin's with Spidey. The Joker views it more as a game and actually wants to kill everyone EXCEPT Batman. Whereas Norman is much more like if Luthor were bipolar. Except that he doesn't BLAME his failure on Spidey exactly. It's more like Norman's elaborate way of denying his illness, the real reason for his failures in family and business. Unlike Luthor, he doesn't blame this on the hero--he takes it out on him. I think you might best look at Norman as an abuser writ large.