I would even go as far as to say that they are more important than the protagonist. Let me give you a classic example: In the little mermaid by Disney, Ariel has the personality of a wet blanket. However, we still root for her to get the even more boring prince. This is all because Ursula is such a good villain. She is charmingly evil and evokes a lot of emotion. In my opinion, this applies to all stories that have the protagonist vs. antagonist setup and even to stories where the protagonist is an anti hero. If the protagonist has conflict within themselves, then they have to be compelling. In comparison, many stories (mostly trope heavy mangas) rely on having a protagonist with a sad backstory and common sense and then don't give the antagonist a full personality/motive/backstory. To me, this just makes the story annoying, much more so than if the roles were reversed and the protagonist were boring and the villain cool. Side tangent: I care less about the villain's personality if they are really hot
If a villain is charismatic enough, it can even make up for a boring protagonist e.g. Loki from Thor, Joker from The Dark Knight. I think a good villain can also be a twisted reflection of the protagonist e.g. Moriarty from Sherlock Holmes. The importance of a great villain is even more evident in rpg games where the player character doesn't have much of a personality, e.g. Ganon from Zelda, Sephiroth from FFVII, Emet-Selch from FFXIV: Shadowbringers, Andrew Ryan from Bioshock, GLaDOS from Portal.
Man I agree, like look at Silco from Arcane, dude is absolutely insane and does the most terrible things but he's so enjoyable as a character as well. Villains need to be given their own personality and backstories in order for them to hit properly.