Dude, why cut off the rest of my post.
i read the book once, 30 years ago.
As far as i can remember, Feyd is practically nonexistent in the book as an actual character. We're point-blank told "killing this guy means a lot to Paul, by the way, because it's got something to do with that
vendetta we've briefly mentioned before, just buy it you don't need any explanation".
And it's ok because the killing of Feyd is not plot-decisive. Paul's already conquered everything and everyone when he fights Feyd and nothing changes *because* of it.
A ton of characters are unidimensional in the book (and in the Lynch film) because they are supporting characters. Tufir doesn't change. Duncan doesn't change. Gurney doesn't change. Leto doesn't change. Jessica pretty much remains the same, she seems a bit more affirmative in her role as the Fremen's Sayyadina but she doesn't actually DO anything.
Raban goes from violent to terrified after Muaddib starts destroying the spice production, the Baron loses it when he thinks he has won, but Dune isn't a story about character arcs.
.. if you recall, among my many criticisms of the "Dune 1" film, is that horrible scene where Momoa / Duncan Idaho meets Paul on Arrakis, and he just grossly sticks out from the scene, he's an absolutely vulgar character that is so completely, ridiculously out of place from the setting, they might as well have made him into a GymBro(tm) complete with whey protein and energy drink.
In the book, and in the Lynch version, these characters are important because of what they represent.
While i don't consider Herbert to be a literary genius, he does well in implying the importance of some background aspects of his story, and setting up a believable world where these barely-described "facts" impact or force the decisions of the main characters. Tufir isn't important because he's Tufir, he's important because he is a HUMAN MENTAT. This in turn excuses why this space-faring empire has machines that look like they belong on a set of an S&M film. The same applies for the Bene Gesserit's ability to influence genetic selection at birth (and the not-mentioned-in-the-film religious propaganda that ensures Paul fits within "the prophecy", instead of being a fucking White Saviour), the importance of the Space Guild and why they (together with CHOAM and the Houses) get to threaten the Emperor, and a shitload more.
Which is also why Lynch was smart enough to add stuff like the Weirding Modules. Or Paul teleporting the water of Caladan onto Arrakis. Because this stuff simply cannot fit into the film, not if you make it 3 hours long, not if you make it 5 hours long, because it can't just be LONG, it also needs to be interesting, and while stuff like the Bulterian Jihad works well as a background, world-building element, it's not really something that you want to have on-screen with the same relevance as the main plot.