Another reason why Faramir didn't fall to the Ring was because he favoured the teachings of Gandalf over Denethor. He was less of a battle commander (though he was still a great one) than his brother. So what Boromir saw as a weapon to use against the enemy, Faramir saw it as a weapon that only the enemy could use.
No one is arguing that Faramir should have succumbed to the Ring, only that it works better if he is at least tempted and has to struggle with it. Everyone else in the books has to fight the temptation of the ring. Gandalf, Elrond, Galadriel, Aragorn, Boromir (looses), all the way down to Sam, is tempted by the blasted thing. Not Faramir. In the books he is just "huh, the Ring of Power. Better give this little short guy some help if we want to win this war." Of course he should resist the temptation in the end, that is the whole point of having the 2 brothers, so one can fall and one can resist, but resisting has very little emotional resonance with an audience if it is accomplished with no effort like in the books.
While it is true that Tom didn't add much, he was the one who gave them the Barrow-Blades. Without them, the whole "No man can kill me" then a woman just stabbing him in the face, killing him, doesn't really make much sense.
All Merry did with the Barrow Blade was distract the Witch King. True, in the book he was only able to do that because of the power of his blade but so what. There is no good way to convey visually that those blades were more potent vs the King of Angmar than other magic blades would be. It is a difference between
"The WK is about to kill Eowyn when Merry stabs him in the knee, distracting him long enough for Eowyn to deliver the killing blow."
"The WK is about to kill Eowyn when Merry stabs him in the knee with his special sword that requires 30 minutes of backstory to explain, distracting him long enough for Eowyn to deliver the killing blow."
The main point was there, Merry hurt him, distracting him enough for Eowyn to kill him. I was considerably more annoyed that the blow didn't incapacitate Merry to the point that he couldn't go with the armies to the Black Gate, though I understand the reasons for that decision.
Yes, the Dead ended the battle sooner, but it would have been pretty easy to explain the fiefs,
It would have been a pain in the butt to try and explain the Gondorian political system well enough for people who have never read the books to have a clue what is up with them. It basically took a whole chapter just to explain who these people all are in the books.