I've always viewed Paarthunax as Dovah kind's last hope of being redeemed. I mean, if he overcame the violence instilled in him by his brother, why couldn't other dragons? I foresee mortalkind and dragons one day coexisting.
I wasn't aware of the scene of him after defeating Alduin, so it seems my suspicions are correct; Paarthunax is the leader dovah kind needs to steer them to a path of peace and wisdom. I refuse for this reason to believe the dragons are really born violent. I mean Alduin's father, after all, is GOD(one of). He's the first dragon, and the same guy who banished Mehrunes Dagon.