We don’t know if Homer actually wrote these hymns that were attributed to him. So, (A) doesn’t tell us anything about whether the same writer could or would write separate works that differ in tone, vocabulary, and other details.

Just because the Iliad and the Odyssey have suffered from “minor copying errors” doesn’t change the fact that the two poems differ greatly in tone, vocabulary, and other details. So the question of whether they might have been written by the same author remains.

By presenting works by the same modern writer that differ greatly in tone, vocabulary, and other details, (C) proves that the author’s assumption (that two works that differ in these respects can’t be by the same writer) cannot be true. So, the author’s conclusion doesn’t follow.

The fact that parts of a work vary in these ways doesn't answer the question of authorship. Perhaps, for example, the work had multiple authors. We need an answer that addresses the assumption that works with such differences can't have been written by the same person.

By suggesting that many poets contributed to the poems, (E) further argues against the idea that the Iliad and Odyssey were written by a single author. So it doesn't weaken the author's conclusion.