C. E. M. Joad quote

[caiusbeerquitius]

Virgil's whole 12 books used to be memorized by heart at Latin secondary schools

Yes, but if you pop the "cui bono" question, it may be so because of completely other reasons than its subjective quality.

For instance one book can sound more dignified than another, can impress mighty emotions or be stale and listless, can deal with higher, more noble, or petty themes etc. There are certain objective criteria for measurement of literature.

But IMO none of those you listed actually belongs to the category "objective".