I always considered Baigan to be "just-off" the mark. Baigan likely comes from a high and noble line of Royal Guard Corps and may feel as if Kain and Cecil are beneath him. Possibly in feeling resentment towards Kain and Cecil as what he saw as favoritism from the King of Baron he allowed this jealousy to consume him, taking advantage of that the Cagnazzo posing as King of Baron may have played into Baigan's inadequacies, fooling him all around, and eventually convincing him to give up his humanity to become a better soldier for Golbez.
What I find really interesting is that Baigan is supposed to come off as immensely polite in the original game (in a proper translation, not our SNES version). Even when he's revealed to be a monster he doesn't lose his dignity. "Beigan: Oh, please don?t speak of him like that. He has given me a wonderful gift, the kind man that he is. This magnificent power!"
For Baigan to join Cecil I think it would be necessary to show that the two may have more of a bond than the original game lets on, of the four (Cecil, Kain, Rosa, and Baigan) he seems to have been the odd one out, but was still given high position (Rosa is actually the leader of the White Mage Corps in Baron, while never said in the game, the setting mentions this and is subtly referenced by the Red Wings and White Mage Corps attending the wedding of Cecil and Rosa in the DS version), I don't think its necessary to change Baigan's upbringing though. I do like the idea of a fake Baigan who lead the Royal Guard Corps to their untimely deaths though. This would make sense on why the real Baigan was locked up.
