Is The Silmarillion a "downer"

[Formendacil]

Originally Posted by Ingwe

I believe that the Silmarillion was not only written to entertain but also to further explain the troubles in Middle Earth in the Third Age

That isn't strictly true, by any means. What you say might explain the Appendices or parts of Unfinished Tales, but the Silmarillion pre-dates the Lord of the Rings by twenty years. And in Tolkien's mind, it was his primary work, which got caught up by association with the world of the Hobbit, thus producing the Lord of the Rings. Quite apart from being an explanation of our beloved novel, it was a source-work.