Grond: I think you've rather hit the nail on the head with your assessment. That is, I think you've identified one of the key failures of the movies. There are many who have defended
Arwen's increased role, especially in
Fellowship, claiming either that it is a relatively minor change that does not distort the plot or, even more outrageously, that it is all based somehow on the Appendices. Both of these arguments miss something fundamental.
There are two sorts of ill effects that arise from the alterations to Arwen's role. The first simply incluces all those ways in which Arwen's character was changed, or the actual
events of the story altered. So instead of
Glorfindel we have Arwen. Instead of being the character
Tolkien described, she's some kind of Xena-like warrior. Instead of
Narsil being reforged before the Fellowship sets out, it's reforged later. And so forth.
Those changes are unfortunate enough in themselves. But what Arwen's defenders seem to miss is the second sort of thing that results from the changes: the distortion of
other characters and of the very nature of the story. While Arwen is being made commercially viable and standing up to the
Nazgul (with some poorly-written bit of Hollywood cliche that never could have come out of one of Tolkien's characters),
Frodo is being very seriously weakened as a character. Turning around and confronting
the Black Riders at the Ford is one of the key moments in Frodo's character arc, and one of the few
places where he is actually very heroic. The few instances like these (another is in the Barrow, but of course that's gone too) are needed early on, since he spends most of
Return of the King doing little other than being extremely weary. Moreover, his early instances of heroism must contrast with his pacifism and resignation at the end. In the movie, Frodo came across very weakly, in part because one of his key moments was stolen by Arwen. As Grond pointed out, Arwen's increased role has had a similar weakening effect on
Aragorn's character.
The change in
Faramir has a very similar effect. In the book, there was a very important contrast between
Boromir and Faramir,
the one who went to the Council and the one who was meant to go, the one who failed to resist temptation and the one who succeeded. There may still be a hint of contrast between them in the movie, but its point is gone. More importantly, Faramir is supposed to represent (along with
Eomer and Aragorn) the hope that is left in
Men. The point is that there are those who will do the right thing, who will overcome temptation. This is lost in the movie.
It seems that Jackson (and Walsh and Boyens) are missing something essential. That is, when you make a change to the plot, or to a character, that change has effects, often subtle effects, throughout the rest of the films. Increasing Arwen's role doesn't just increase Arwen's role - it weakens other roles. The same for Faramir's change. This is one of the key weaknesses of the movies.