It could be argued that Virgil's Aeneid is derivative yet is Homer's Iliad entirely original?

Towards the end of his life Virgil wanted the Aeneid burned. This was perhaps because being a perfectionist he felt this epic poem needed even more time than the eleven years already given to this work. ‘Homer’ is more of a mystery but the Iliad has been added to over time. The wrath of Achilles, the rout of the Greeks, the slaying of Patroklus, Achilles killing Polydorus and Lykaon and Hektor – these could be the core of the first poem but other elements have a change of attitude. So is everything in literature derivative? Is there nothing original on this planet?