With Dracula, I have zero problem writing him as a totally unsympathetic villain who is a complete monster. But Carmilla? Spoiled brat nineteen year old who has never heard the word no.
People seem to really forget that Carmilla is nineteen, forever. That's a much different brain than say, twenty five forever. Or even twenty one forever. She's supremely selfish, dramatic, sarcastic, romantic, and furious BECAUSE she's nineteen forever.
Dracula has suppressed his emotions. Carmilla IS her emotions.
Dracula also mostly practices moderation, not because he has any respect for humanity but because being careful has kept him alive. (The most wanton slaughter he commits in the book is the crew of the Demeter and that can be argued as his needing to regain his full strength and leave no witnesses to his arrival in England.)
Carmilla? She says she loves Laura and drinks her. She said she loved Bertha and drained her. She eats all the village girls so that she can be with Laura longer, knowing that Laura is simultaneously her best friend and her favorite delicacy. Plus in her backstory, she was historically such a problem that the crown sent a knight to destroy her.
Dracula is more dangerous, but Carmilla is greedier.
Which ties right back to how Dracula is an unfeeling, cruel old man who vaguely remembers how love felt once, and Carmilla is, at heart, a scared, lonely, passionate, foolish, snarky, hotheaded teenager. She literally cannot learn to be "better". She is who she is. And it is very funny when she is written as a suave older femme fatale because yeah. In her dreams she's Gloria Holden (the actress who played Countess Zaleska, Dracula's daughter, in the 1936 Universal horror movie). In reality she's a mess.
And that's why we like her.