Bit of a naff comparison really. Did half the world die in the process of Bond saving it? You need to remember its high fantasy written in the thirties. I feel you are missing the entire premise of the film. You're right, they have a near undefeatable army of the undead, several heroes with supernatural abilities, the most powerful wizard in the world, and guess what? They STILL rely on an unassuming hobbit to save the world. 'Even the smallest person can change the course of the future.'
You could make that over simplification for practically any film. 'We all know Michael is going to become the Godfather, why didn't we just skip the crap and have him murder the heads of all the crime families and we could be done in 5 minutes.' It's almost as if his journey is as important as the destination?
Firstly, because the cinematography and the scenes in those battles is fecking incredible. Even now watching the Ride of the Rohirrim and Gimli blowing the horn of helm hammerhand gives me goosebumps. Secondly, a hell of a lot more happens in those battles other than 'they fight.' They go a significant way in shaping what the world will be like after the fall of Sauron. From Aragorns journey to claiming his place as king, to Bormomirs salvation, to the renewed alliance between elves and men, always the story is being progressed, the sense of doom is heightened, and the characters develop. The insular wants and needs of the Individuals who rule middle earth either change as they see the bigger picture, or those individuals die, like with the case of Denethor. It immerses you in this world where these characters band together against impossible odds, right up until the battle of the black gate.