I probably didn't write it in the best way, and it ended a bit confusing.
What I meant is that Civ4's leaders behaved more in the way that a "real" leader would make : like if he's trying to rule a nation, following some personnal preferences.
Civ5's leaders behave more like players trying to win a game.
But we need the AI to try to beat us. Ok, so they have different traits or specialties. Fine. If the purple civ is supposed to be good at culture, let them be ahead of me in SP and I will try to catch up and win. If the red civ is suppose to be good at military, let them be aggresive in attacking me, putting me on the defense. If the green civ is supposed to be good at expansion and growth, let them be ahead of me on the tech tree and I will try to beat you to UN. If the brown civ is supposed to be good at production, let them try to beat me to the spaceship. If any of the civs are more well-rounded, let them be unpredictable and surprise me in jumping ahead in one of the victories. I do not know what "rule a nation" means in civ, nor should it mean anything except trying to beat me. It could not do that well without cheating in Civ4 and in Civ5, it doesn't appear they are able to be that good at anything, without luck.