He was consumed by the devil. He was hollowed out and dehumanized by being forcefully assimilated. He's making a futile attempt to save himself by bringing in Sammie when in fact he's already lost his soul.
He can perform the music and art of his culture, but it's not for the sake of his heritage or to bring people together in community. It's to fill an emptiness within himself brought about by the vampire that turned him.
He was made into a monster, forced into living a half life, convinced that he can undo the harm done to him by harming others.
I don't see him as the personification of the devil so much as a casualty of the devil.
You see in the movie that the other people who become vampires act in ways they wouldn't otherwise.
His Irish heritage wasn't vilified and at no point did a character conflate his heritage with his villainous acts.
The rest of the cast were wary of him more because he was white in a space for people of color.
Fictional evil characters are extremely popular in media.
Jack O'Connell is a talented, conventionally attractive man and his character was powerful, charismatic, and compelling.
He was supernaturally evil and that evil wasn't tied to him being Irish. He was depicted as more sympathetic than the KKK who sought to kill out of hate instead of a supernatural compulsion.