You can argue that much of the books can be eliminated because they're just not Hollywood, reading is for boomers after all.
The origin of the blade is relevant because they nearly died in getting it, and because it came from the tomb of a prince who himself died battling the Witch King, so in a sense he obtained vengeance from beyond the grave. "Wow, this sword just turned out to be magic, what a coincidence" isn't nearly the same thing.
Film--even a whole trilogy of films--is a different medium from books. Books are in general much more tolerant of diversions that don't move the story forward. Bombadil was pretty much a diversion.
The films also had to deal with the fact that the LoTR books had a lot of material after the ring was destroyed--and that's not even counting all the material in the appendix of RoTK. Say whatever positive things you like about LoTR but the narrative structure of RoTK in particular is a bit of a mess.
I don't think it was "a mess" (just reread it this spring). Books support a lot more alternatives to structuring a story than most movies, with their tight time limits, want to explore.
That doesn't mean movies are better: in fact, movies are clearly more limited and worse, from the point of view of telling long, complicated stories. But people enjoy movies (me too), so... compromises.
The origin of the blade is relevant because they nearly died in getting it, and because it came from the tomb of a prince who himself died battling the Witch King, so in a sense he obtained vengeance from beyond the grave. "Wow, this sword just turned out to be magic, what a coincidence" isn't nearly the same thing.