We don’t know that oral traditions are more “accurate.” They do have less potential for confusion, but is that the same thing as being more accurate? It’s not clear. In any case, even IF oral traditions were more accurate, (A) would only establish that oral traditions tend to breed “mental self-reliance.” But is that a good thing? That’s the whole missing piece — sure, you can say that written traditions encourage a bunch of qualities. But are those qualities BETTER than the qualities encouraged by written traditions? That’s what we don’t know.

(B) asserts that populations that can read/write should try to communicate more efficiently. But is there anything about oral traditions that we should prefer over written ones? Maybe populations that use oral traditions also need to make efforts to communicate efficiently.

We’re trying to argue that one tradition is preferable to another. A blanket statement about “tradition” being more valuable than something else doesn’t help us say that one kind of tradition is better than another.

“Economy of expression” refers to being concise and avoiding unnecessary expressions. “Verbosity” refers to the opposite of that. So (E) establishes that being concise and avoiding unnecessary expressions is better than saying more than is necessary. That strengthens the argument by affirming that one of the features of oral traditions is better than a feature of written traditions.

We’re trying to show that oral traditions are more preferable than written ones. (E) concerns what ideas should be discussed; but that doesn’t help us identify one kind of tradition as better than another.