People have been wanting to see Vader kill Rebels with his own hands for decades. If anything Gareth knew exactly what most people wanted.
This is exactly why it felt like a fan film to me. It’s not something Vader would have done in the original films, it’s what the fans wanted him to do. It’s the same reasoning we had CGI Yoda bounce around in Attack of the Clones.
As Ronster said before no one wanted that but George and secondly given the limited time he had yes he would. It can definitely be for fan pleasing purposes, consistency with his character and to add tension and a sense of urgency to the climax of the film. Also let’s not forget that Vader got brutish with Luke in ESB.