Apparently discord is more a pathetic prankster than a evil villain.
The guy is omnipotent, capable of making anything he wants come true. Not the first definition of pathetic that comes to mind.
That's the difference, he couldn't create friendship because he didn't know what it was. Once he's mastered the art, he can feel free to go back to doing his own thing, now with a friend who won't hold him back. Look at what he started with Tirek. If big red hadn't caught him by surprise, Discord would have gone back to ruling Equestria.