NeverarGreat said:
The movie could be from the point of view of Bilbo, who gets knocked out during the battle and misses the fight. He recovers afterwards and finds Thorin dying on the battlefield. It's more similar to the book in that way.
Some of the less-than-legal one film edits floating around have gone this route, and it simply doesn't work. The main character getting knocked out and missing a huge chunk of climax might work in a book (though I'd argue it doesn't) but in a film it's hugely deflating. Especially when it's the climax of so much story. I'm all for being true to the book, but this is one of the few instances where the changes were an improvement. The fight is a bit overblown but at least it was something.
Imagine if Aragorn got knocked out during Helm's Deep, then he wakes up and Gandalf is like "Oh you missed it, we saved you."? Or that episode of Game of Thrones Season 1 where they did this exact thing with Tyrion?