The study of eloquence concerns more than producing rhyme, paronomasia or antithesis: the freshness of imagery and expression also matters. The discussion of borrowing examines originality, suitability of meaning and the quality of poetic transformation.
This is a classical rhetorical and critical taxonomy, not a modern legal finding. To classify an example as copying, taking or coincidence, one must first examine its form and thought.
The topic therefore belongs to the wider evaluation of eloquence without becoming another device such as sajʿ or jinās.