Honestly, not sure what class creature type Christian from Midsommar would get. Peasant represents he's some goof of a victim who is of no importance, but that may be too boring and obvious choice for fans of the reference to appreciate. As he was still studying, I get a scholarly vibe and given studying anthropology, advisor might be the most direct real-world translation of the character's literal class equivlanet. However, Christian is the major villain of Midsommar, and what class represents that? As Outlaws of Thunder Junction has shown, there's no one class type for villains. Rogue would be perhaps the only one that offers a villainy that Christian's patheticness could perhaps be accounted on the angle that he is a moral rogue.
I'm sticking with peasant for now.

Christian is not the major villain of Midsommar. It would be quite reductive to say the movie has a thing like that. He's one in an ensemble of tragic characters with appropriately tragic flaws who plays an antagonistic role to multiple people/groups.

I really feel like leaving off the class altogether would serve to focus on the fact that at the moment of sacrifice his scholarly background doesn't matter. He's just a Human sacrifice after all.

I disagree about Christian being the main villain of Midsommar. Dani is the protagonist and Christian's relationship with Dani throughout the film casts him as the villain of Dani's story. For the film as a whole, the Harga may be considered major villain, but through Dani's perspective the cult is a better alternative than Christian.
I wouldn't consider Christian tragic based on any of the events that occur within the film. Yes, he was a victim, but by nature of being the primary human antagonist towards the protagonist and he has more characterization than his cardboard friends. For what its worth, between Midsommar and Hereditary, I don't think Ari Aster attempts to develop any character who isn't the main character beyond the cardboard character archetype assigned to them, so he ends up being the second-most fleshed out character in the film imo. He was a pathetic unmotivated individual incapable of doing anything on his own. The scene between him and his one friend over writing about the Harga showed that Christian was downright parasitic.