A big feature of Tarantino's movies is routinely to subvert the genre while also celebrating it. Reservoir Dogs is a "heist movie" where we never see the actual heist and even the "planning scenes" skip virtually all the details of the actual crime and are mostly just about the characters interacting. By comparison Django is more of a Western, in that it gives you basically every scene and trope you expect from one, but also puts a giant central emphasis on slavery where most of the old Westerns bowdlerized it, and the elephant in the room for the time period was left off-screen.
Sinners is certainly also about cultural oppression, colonization and exploitation, and the legacy of slavery, but I don't think that makes it any less of a vampire movie. The vampires are also predators and exploiters, and Remmick represents the exploited who assimilates into the power structure enough to become an exploiter in turn. Much as the Irish in America integrated sufficiently to start being considered "white" and participate in racist power structures as oppressors instead of the oppressed. Stack, too, is preyed on and becomes a predator himself, where Smoke refuses, does his best to protect others, and claims his (literal or figurative) heaven of reunion with his loving family. In Dracula, the vampire is ALSO a metaphor, for disease and infection, for sexual repression and feared expression, for predatory aristocrats... But that doesn't make it any less a vampire story.