That's an interesting take. I haven't read LOTR but my friends who are big time fans of the books just loved the screen adaption of LOTR.
The screen adaptation of the LOTR was very well done, but it is still limited as a movie.
The son is correct, the artistry and magic of the books was not, and can never be, captured by a movie. To read the trilogy for the first time, hopefully before one sees the movies is a great experience. It is fulfilling and broadening at the same time. The movies are great entertainment, but they don’t replace the work itself and the son should not expect them to do something that impossible.
The impossibility is a credit to the original work not a criticism of the movie’s execution.
When I saw the first one, I was amazed that they’d portrayed every single character, even the Orcs, exactly as I imagined them while reading the books. I think they did a damn fine job, at least in the LOTR trilogy.