[Question] How much stupider than humans can AI be and still kill us all through sheer numbers and resource access?

It is reasonably clear that not just a super-human but “just” a human-level AGI that can “clone itself” can defeat humanity through concerted effort and determination, should they choose to. I wonder how much less intelligent than an average human an AGI can be and still have no trouble making short work of humanity? An army of e-chimps? An army of e-chipmunks?