A speaker wishes to express courage. “Huwa ka-l-asadi fī sh-shajāʿah” openly identifies the comparison and its shared quality. “Raʾaytu asadan yuqātil” can be an explicit metaphor when its context makes clear that “lion” denotes a brave person.
Both may praise bravery, but their mechanisms differ: one asserts resemblance; the other uses the model term for the human referent. A shared communicative goal does not make the rhetorical categories interchangeable.