Yeah, I definitely would never describe the prose in LOTR as not serious. In The Hobbit absolutely (and to be fair it
was a children's book), but not LOTR. One of the things that the book LOTR does best compared to the movies is the prose!
For example, compare the book and film versions of the scene in Return of the King when Eowyn confronts (and kills) the Witch-King. In the book it goes like this:
"Then out of the blackness in [Merry's] mind he thought that he heard Dernhelm speaking; yet now the voice seemed strange, recalling some other voice that he had known.
"'Begone, foul dwimmerlaik, lord of carrion! Leave the dead in peace!'
"A cold voice answered: 'Come not between the Nazgûl and his prey! Or he will not slay thee in thy turn. He will bear thee away to the houses of lamentation, beyond all darkness, where thy flesh shall be devoured, and thy shrivelled mind be left naked to the Lidless Eye.'
"A sword rang as it was drawn. 'Do what you will; but I will hinder it, if I may.'
"'Hinder me? Thou fool. No living man may hinder me!'
"Then Merry heard of all sounds in that hour the strangest. It seemed that Dernhelm laughed, and the clear voice was like the ring of steel. 'But no living man am I! You look upon a woman. Éowyn I am, Éomund's daughter. You stand between me and my lord and kin. Begone, if you be not deathless! For living or dark undead, I will smite you, if you touch him.'"
Now compare the movie version of this scene. Obviously there's no narration, but the dialogue is significantly compressed and loses all its flavor.
"I will kill you if you touch him!"
"You fool! No man can kill me!"
(Eowyn removes her helmet) "I am no man!"
I don't blame Peter Jackson for the change. His movies got a lot wrong when adapting the book, but this wasn't one of those things. The original dialogue, even if condensed, would not work very well for a movie. But even though the change was necessary, it still reduces the dialogue from something epic (in the literal sense of the word) and beautiful, into just a generic action hero moment. The book version is just so much better.
And this is not an isolated incident, either. Throughout the movie trilogy, scenes which were written with beautiful prose in the book have most of their beauty taken away due to the need to write dialogue in a way that works better in a movie. It's necessary, for sure! Even so, however, it means that I can't agree with the claim that the LOTR movies handle such things better than the book's prose does.