I think if the Vader scene had some lead-up, such as a scene where the Rebels worry about this ‘Vader’ character that seems to be close to discovering their operation, then it would work a lot better. As it is it comes rather out of left field in the context of the film and feels gratuitous in its horror and violence. I wouldn’t say it portrays Vader as a cool badass, but I understand why some would think this way.
In any case, RO’s problems are bigger than this one scene.