UNPOPULAR OPINION
Every single added Darth Anybody, Sith Inquisitor, Sith Witch, Sith whatever – the Emperor excluded – made Darth Vader less and less unique during the decades.
Don’t wholly disagree. That said, I’ll always defend the Imperial Inquisitor concept. Makes little sense that Vader would be the only Jedi to turn to the dark side and join the Empire.