In your opinion, which hero has the most charisma in the campaign?

He definitely conquered Igg-Shail for himself. Isabelle had nothing to do with it. As for why he spent so much time in the portal, that's easily explained. When he came to Malsara, he made something of a deal or a wager with her. He said he wanted power and knowledge, and she replied that she would give him both if he united the clans and found the Tear of Ash. He agreed, fulfilled his part of the deal, received an army for himself, and then decided to pass on his responsibilities to Ilia, who would later become his right hand.