But then you're no longer doing anything that comments on Tolkien's actual work

It looks like it's basically shifting the view of the original LotR into an in-universe text with some serious history-as-written-by-the-winners bias instead of objectively described stuff that really happens. Haven't read the book yet, but this seems like a pretty interesting approach to me. It's a fun twist on the generally very literal-minded way speculative fiction is read.