That doesn’t have to be the case. Take Farscape as an example, they had fantastic main villain in that show, and you could very much understand his motivations, and even find him relatable in some ways. Yet, it didn’t detract from him being a villain and having some of the best writing.
Definitely pure evil. If you make a villain too sympathetic then the writing inevitably takes a nose dive because “Why are we fighting?”
If that’s what a sympathetic villain made you feel then they clearly weren’t written well.
That doesn’t have to be the case. Take Farscape as an example, they had fantastic main villain in that show, and you could very much understand his motivations, and even find him relatable in some ways. Yet, it didn’t detract from him being a villain and having some of the best writing.