At the same time, to argue Syn's point, I don't think we should be limited just because of tradition. Otherwise, we'd have lost tons of really great development with wiegeabo's Sinestro during the seasons where he was trying to do the right thing, rather than be malicious or hateful of The Green Lantern Corps/Guardians. Now, say wiegeabo had a really big event happen in his life and he was unable to continue with Sinestro midway through the arc. No new player would be able to pick up Sinestro without either continuing another person's arc or, as you said, undoing all of someone's hard work. Does that mean wieg should have never taken the effort to make Sinestro a genuinely interesting character and explore him in his own way?
See, I don't think so. We should be creatively free to take the basic templates and mend them through experiences, fights, tragedies, and soforth in interesting ways. That's how characters grow. Is it a downer for new players? Sure, I'll totally admit that. But at the same time, I think that's why we have RPG's like One Universe, where Sinestro is still a Corpsman destined to become a bad guy. Or Ultimate DC, where you can take a character and do whatever you want with them from the beginning. Or even the short-term RPG's, now, where we'll get other people trying out characters like Superman, Batman, and the like. I think that we have enough variety to warrant creative freedom.