When Vader is angry, he’s definitely colder than when young Anakin was angry. When he was angry, young Anakin showed his emotions more openly, unlike Vader who showed his anger much more coldly. However, in my opinion they are not different characters, but simply two different behaviors of the same character. After all, when Vader was already a servant of the Emperor, he had nothing left. I think his cold and calculating behavior is due to the fact that he was completely lonely and had nothing left to lose, he no longer had anything that made him feel really connected to anything, he had nothing that made him feel that his emotions were really worth expressing . Only when he realized that Luke was his son he did begin to express his emotions more openly, which is why in Return of the Jedi we see him acting a bit more like Hayden from the Prequels. There’s no contradiction between the two attitudes. When a person loses everything and has nothing to care about, it often happens that this person becomes much colder and more reserved, and that he shows his anger less emotionally than when he still had something that mattered to him. This is something that often happens in many movies and with many characters, and it’s not a contradiction.