I'd say that Taravangian is just about the boldest character Brandon's made. He killed tens or hundreds of thousands of people because he genuinely believed that they would all die anyways. In return for killing so many people, all he asked of Odium was the salvation of his city. He had a goal, and he stuck to that goal. You mention Dalinar's character growth, saying that it would be bolder if he still thought that the Rift had been the correct decision; Taravangian is the kind of man that thinks the rift was the correct decision, and, despite attempts by several sympathetic characters, he has not changed. Upon taking up a shard, instead of coming to the realization that he had been wrong to kill those people and stopping the war between mankind and the singers, he immediately began planning how to use those people he had wanted to save in order to "save" the people of the entire Cosmere. He is a far bolder character than Kelsier, who has been changed by characters like Vin.